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N° BLOOMEI 


1 Kee — & 














inl 


THE CHEMISTRY OF 
PAINTS, PIGMENTS AND VARNISHES 





THE 
CHEMISTRY OF PAINTS, 
PIGMENTS & VARNISHES 


ve ES) Jk a ee 
J. GAULD. EEARN; MSc.) AIG; Fics. 


(CHIEF CHEMIST: ¥@ MESSRS) WALTER CARSON (AND SONS) 


NEW YORK 


VAN NOSTRAND COMPANY 
EIGHT WARREN STREET 


1924 





‘- 


ted iu Great Britade 


Ni 


rE: 


Made and P 


by Turnbull & Spears, Edinburgh 











PREFACE 


In few industries of comparable size and importance were scientific methods applied 
so late as in the Paint and Varnish Industry, and in none has the value of these 
methods been more clearly demonstrated. To-day the industry is one of the most 
highly specialised: empirical methods of manufacture have been superseded by 
processes based on detailed research work by trained specialists; many new raw 
materials have been introduced ; and, in the different branches of the industry, 
the attack on the many and fascinating problems presented is being pursued 
constantly and scientifically. Numerous difficulties which baffled the patience and 
skill of the earlier chemists have been overcome. To instance a few of these, the 
Lake manufacturer has now at his command a range of synthetic dye-stufis of a 
permanency and colour stability undreamed of twenty-five years ago; new and 
more efficient solvents have been discovered ; celluloid and nitro-cellulose lacquers 
have been introduced ; methods of application by spraying and dipping have been 
perfected, and the synthetic production, on a commercial basis, of artificial 
resins seems to be in sight. 

These are but a few of the more important of recent developments, and it has 
become a matter of no small difficulty for those interested in the industry to keep 
abreast with the numerous new processes. The “ Chemistry of Paints, Pigments 
and Varnishes” has been written in the hope that it will be of assistance to works 
managers and to students in obtaining both a general survey of the industry as a 
whole and an account of the modern technical processes and of the chemistry of the 
raw materials employed. In addition to those actually engaged in the different 
branches of the industry, I trust that it will be found useful also to analysts called 
upon to test these materials, and to architects and others who have to specify them 
for various protective uses. With this object detailed raethods of analysis have 
been given, and the specifications included will enable users of the materials to 
judge whether various products and specialities offered to them reach the standard 
required and are suitable for the purpose in view. 

It will be understood that it has not been possible, nor was it the intention, 
to include in a book of this nature more than a brief description of the different 
types of machinery involved. Any reader desirous of obtainimg more detailed 

v 


PAE OD 


vi THE CHEMISTRY OF PAINTS 


information on these matters is referred to the authorities mentioned in the 
Bibliography at the end of the book. 

I am indebted to Mr Alwyne Meade, the author of “ Modern Gasworks 
Practice,” for much valuable advice and encouragement in the preparation of 
this book, and to the manufacturers noted in the text who have kindly furnished 
illustrations. In conclusion I have to express my thanks to my brother, Mr James 
Bearn, who has given me great assistance in revising the text. 


J. tee 


Lonpon, October 1923 


CHAP. 


Tl. 


IV. 


vi. 


VII. 


Vil. 


CONTENTS 


PREFACE 
PART I 
PAINTS : THEIR COMPOSITION, PROPERTIES AND USES 
. INTRODUCTORY 
. MANUFACTURE OF PAINTS 


Pugging—Grinding—Mixing Renter 


WHITE AND COLOURED Paints, ENAMELS, ANTI-CORROSIVE AND ANTI-FOULING 


PAINTS 


Paste Colours—Ready-mixed Pups Merial Paints, ener or Japans— 
Agricultural and Implement Paints, Dipping and Spraying Paints—Staining 
and Graining Colours—Anti-Corrosion Paints—Anti-Fouling Compositions 
—Metallic Paints—Luminous Paints. 


DISTEMPERS, COLD WATER PAINTS 
Dry Distempers—Paste Fees itera Fire neces Paints. 


. THe ANALYSIS AND VALUATION OF PAINTS AND ENAMELS 


Chemical Analysis—Analysis of the Paint Vehicle—Analysis of the Poon 
White Paints—Coloured Paints—EHstimation of Water in eae Soe 
Tests. 


PART II 


THE INORGANIC AND ORGANIC PIGMENTS. THEIR PREPARATION 
AND PROPERTIES 


Tar Ware PIGMENTS 


(A) The Naturally occurring , White Pigmetis “7 The White Tyee chew 
Chemical Colours. 


THe YEeLLow INorGanic PIGMENTS : 
(A) The Yellow Earth{Colours—(B) The aren ean Chemical Gian 


Tue Buve PIGMENTS : ‘ 
Ultramarine Blue—Lime eee Peace Blue—Cobalt Blues. 


Vil 


PAGE 


17 


21 


27 


60 


80 


XII. 


XIII. 


XIV. 


XVI. 


XVII. 


XVIII. 


XIX. 


XXI. 


THE CHEMISTRY OF PAINTS 


. THE GREEN INORGANIC PIGMENTS 


(1) The Green Earth Colours—(2) The Manufoncpeal fae Piseliix 


. Tart Rep Inorcanic PIGMENTS 


Red Oxides of Iron. 


. Tat Brown PIGMENTS . 


Raw Umber—Burnt Uinihek Vande ee eqn 


THE Brack PIGMENTS 
The Black Earth Pigments. 


Lakes AND Lake PIGMENT COLOURS 
Lakes from Natural Colouring Matters -Coahined lakaee rakes from Synthetic 
Dye-stufis. 


THe ANALYSIS AND EVALUATION OF PIGMENTS ACCORDING TO THEIR PHYSICAL 
PROPERTIES . 


PART III 


VARNISHES, LACQUERS AND JAPANS 


. INTRODUCTION. CoLoPpHoNy, Sort RzEsins, BALSAMS AND Fosstt Gums 


Raw Materials. 


Dryine Ons 
Linseed Oil. 


SOLVENTS AND DILUENTS 


MANUFACTURE OF OIL VARNISHES 
Rosin Varnishes—Wood Oil Varnishes. 


THE MANUFACTURE OF SPIRIT VARNISHES, CELLULOID VARNISHES, LACQUERS 
AND DOPES . 


. DRIERS OR SICCATIVES 


Lead Driers—Manganese Driers Cobalt reeennes Gosia) in oil or Pasta 
Driers. 


Brunswick Buacks, BLack JAPANS AND STOVING BLACKS 
BIBLIOGRAPHY 
APPENDIX 


INDEX 


PAGE 


94 


108 


121 


125 


133 


151 


160 


174 


194 


216 


232 


239 


251 
255 
257 


269 


LIST OF ILLUSTRATIONS 


PART I 
FIG. PAGE 
1. VERTICAL Pue Minn ; : : : . 2 : : 5 
2. TRIPLE RoLueR Minn : : : ‘ : . facing page 6 
3. Iron Epegz Runner Mu . ; : : : , ; - 6 
4. Cone Parnt Mr. : ; : : ; : : * 18 
5. Liqguip Paint Mixer ; : : ‘ ; - 18 
6. GARDNER’S COMBINED RaPID a hea AND Mae ‘ ' , ; , 18 
7. SOXHLET’S EXTRACTION APPARATUS . , . ; ; ; , 22 
PART II 
8. ELUTRIATOR . ; ; F : ; : : 2 30 
9. ScHROTTER CO, er ‘ : : : : : : ? 32 
10. Waitt Leap Corropine Pot : : f : . ‘ : 4] 
11. PLavson Con~torp Mint (Front View) ; ‘ : ‘ . facing page 62 
12. PLauson CotLoip Minn (Back VIEW) ; E : ) : Ee 62 
13. PLAN oF CoLtourR House . z : : ; : , , 66 
14. Etzevation CoLtour HovseE . : ‘ ; ‘ : ; . 66 
15. PRECIPITATION VAT . , ; ; ; , ; : : 67 
16. PRECIPITATION VAT SHOWING STIRRERS ‘ ; ‘ : : 68 
17. TWELVE-CHAMBER WOODEN FILTER PRESS FOR CoLouRS; FLUSH PLATE AND Daren 
Frame Type; Puates 28 mn. By 21 in. THRovGH EXTRACTION WASHING 
ARRANGEMENT. PLATES FITTED WITH LigNuM Vit Cocks . . facing page 68 
17a. FiuterR Press For CoLtours. 25-1n. Square D TypPr, witH 30 CHAMBERS sa 68 
18, Vacuum Dryina STOVE : ‘ e F z : es 70 
19. Vacuum Dryine STOVE SHOWING THE DOUBLE RECEIVERS, Pinta sine AND 
Vacuum Pump . ‘ : , ; : g S 72 
20. ILLUSTRATION SHOWING METHOD OF FILLING Vacuum Dryine STOVE : ie 72 
21. Sprcrric Gravity BoTTLE . : : ; : : : ae Loe 
22. THE LoviBonD TINTOMETER : : : : : : men, a3: 
23. Microscorr SLIDE WITH REDUCTION TEST . ; : : ‘ . 155 
PART III 
24. ANGLO-AMERICAN ROLLS ; : ‘ ‘ facing page 175 
25. LinspED Heatinac KETTLES OR COOKERS WITH ae Movxipine MAcHIN=S ns 175 
26. ANGLO-AMERICAN PRESS : ; 4 ; ; ; ; Re ey 


1x 


Be THE CHEMISTRY OF PAINTS 
FIG, PAGE 
27. Vinw oF Sonip RoLLeD STEEL Press PLATES, AS SUPPLIED WITH ANGLO-AMERICAN 

PRESS, SHOWING ExnvaTion, LonerrupINAL ELEVATION AND Cross SECTION 

OF THE PLATES BENT COLD : : ; ‘ : facing page 176 
28. Oi ExTRAcTION BY SOLVENTS—VIEW SHOWING EXTRACTION VESSELS, Con- 

DENSER, EVAPORATORS, ETC., IN LARGE EXTRACTION PLANT . & 176 
29. Om ExTRACTION BY SOLVENTS—EVAPORATORS AND CONDENSERS IN LARGE 

EXTRACTION PLANT ; : 5 : < “1 177 
30. REFRACTOMETER 5 : 4 ; ; ; 3 3 Flee Abed | 
31. LinsEED Om Bormine Pan, HEATED BY STEAM - 5 ; . : 184 
32. FULLER’s EartH Or REFINING PLANT A : c ; facing page 189 
33. Rosrn Stitt AND CoNDENSING WoRM : : : : : « 193: 
34. ABEL FrasH Point APPARATUS ; : ‘ : é ; 3. oe 
35. STANDARD DISTILLATION APPARATUS ; : : : : LF 
36. STANDARD ENGLER DISTILLATION FLASK  . A . : : . 285 
37. 60-LB. Gum Runninc Pot; ALumiIniumM ToP WITH FLANGED-ON DETACHABLE 

CorpPER OR SPECIAL BRoNzE BotTTrom . E : : F rey 3 | 
37a. STANDARD 60-LB. ALUMINIUM Gum Pot, sHOWING DIMENSIONS . ;, Pri ease 
378. Gum Runnine Pot. DETACHABLE BoTToM. COVER AND FuME PIPE r ~-, Bas 
38. VaRNISH Pot CovER WITH COMPENSATING LiFT : : Z . 2S 
39. VARNISH PoT CARRIAGE ; A 3 A “ : oe eee 
40. VARNISH Pot CARRIAGE WITH VARNISH Ports : : : facing page 220 
41. VarnisH Fitter PRESS WITH SELF-CONTINUED BELT-DRIVEN PUMP . 35 220 
42. SHARPLE’S VARNISH CENTRIFUGE . ; : : : : » & 2220 
43. STANDARD 130-GALLON ALUMINIUM Ort BortiInc Pot with FLANGED-ON COPPER OR 

Spectra, Bronze Borrom : : : : : a 
44, OstwaLD VISCOMETER : ; : . : ‘ : See 
45. Sprrit VARNISH CHURN : - : : : . 5 wee Ao 


THE CHEMISTRY OF 
PAINTS, PIGMENTS AND VARNISHES 


PAR YI 


Paints: Their Composition, Properties and Uses 


CHAPTER I 


INTRODUCTORY 


Patmnts may be defined generally as liquids which contain solid particles in 
suspension, and which are used both as protective and decorative coatings on the 
surfaces to which they are applied. 

Paints are usually made by grinding the solid particles or pigments in an oil 
or varnish medium to an extremely fine state of sub-division, a small proportion 
of a volatile “thinner,” such as turpentine, being added in order that the paints 
may be spread easily and uniformly. 

The paint medium or vehicle commonly used is composed of a mixture of raw 
and boiled linseed oil, for raw linseed oil if used alone would dry too slowly to be 
satisfactory. 

The rate of drying of paints may, if desired, be accelerated by the addition 
of driers such as sugar of lead (lead acetate) and borate of manganese (see 
Chapter XX._). 

When paints are applied the volatile medium evaporates, leaving behind an 
oil pigment coating, which dries or hardens owing to the absorption of oxygen from 
the air by the oil content. The solidified oil acts as a binder for the pigments and 
holds them in their place. 

The addition of varnish, such as copal varnish, causes the paints to dry off with 
a bright glossy surface; when so treated these paints are known as enamel paints, 
or simply as enamels. 

Besides being sold in the “ ready-mixed ” or liquid state ready for use, paints 
are also’ made in the paste form by grinding the pigments in raw linseed oil. 

Colours ground in oil are prepared for use by thinning down with a suitable 
paint medium composed of raw and boiled linseed oil, with the addition of turpentine 
and a small percentage of driers. 

Sometimes dry colours are described as paints, and specifications are met with 
in which they are described under this designation, as, for example, “ Paint, Chinese 

i) 


2 THE CHEMISTRY OF PAINTS 


Blue, Dry.” The use of the word “ paint” in this way is to be deprecated, for it 
is better to describe all such dry colours as pigments. 

An exception may, perhaps, be made in the case of mixed pigments containing 
driers and made to some particular shade or pattern, as, for instance, ““ Khaki Paint, 
Dry,” with a mixture of, say, white lead, yellow ochre, carbon black, red oxide, 
and which simply requires mixing with a proportion of liquid medium to make 
it ready for use. 

A paint when applied in the form of a thin film or coating should dry off in a 
reasonable time, say 8-12 hours, giving tough, elastic, hard and durable coatings. 

A good quality of paint should be easily applied, cover well, be opaque, or, 
as it is generally described, possess good “ body ”’; it should also be durable on 
exposure, so that it may afford suitable protection to the surfaces to which 
it is applied. 

Paints may also be made to dry with a matt or semi-matt (egg-shell) finish 
by decreasing the amount of oil or varnish content and increasing the proportion 
of volatile thinners. . 

The body and covering power of a paint is dependent on the amount and 
nature of the pigments it contains in suspension; and as a rule the finer the 
state of sub-division of the particles of the pigment the greater the body and 
covering power. 

The durability of a paint is dependent on the nature of the oil or oil varnish 
content, and only pure drying oils should be used in their preparation. 

The addition of rosin or other soft resin varnish mediums will cause the rapid 
deterioration of paint films on exposure to weathering influences, resulting in the 
paints cracking and chipping off after only a few months’ exposure. 

Paint films wear better than oil films, as the latter are somewhat porous, and 
the addition of the pigments tends to make them dry off harder and become more 
impervious to air and moisture. 

Additions of polymerised oils such as blown oils and stand oils to paint mediums 
increase their durability to a remarkable extent, owing to the fact that such films 
on oxidation give highly elastic and waterproof films. The same result is also 
obtained by judicious admixtures of hard copal varnishes and wood oils. 

The protective and anti-corrosive properties of paints vary enormously according 
to their composition. As a rule coloured paints, such as red oxide paints, carbon 
black paints, etc., are found to be more durable than white or light-coloured paints. 

The durability of a paint as regards its protective and wearing properties can 
only be determined by practical exposure tests lasting over several years. 

It has been found that paints containing alkaline or basic pigments and those 
containing chromates are the most efficient in protecting iron-work from corrosion, 
whilst those containing mixtures of white lead and zinc oxide pigments are 
remarkable for their extreme durability and hard-wearing properties. 

The addition of the so-called inert pigments as ‘‘ extenders” to paint, such 
as barytes, silica, and whiting, was formerly looked upon purely and simply as the 
addition of adulterants, but it has been shown as regards some of them that they 


THEIR COMPOSITION, PROPERTIES AND USES 3 


tend to prolong the life of the paint, and are valuable adjuncts provided they are 
used in limited amounts. 

Paints on exposure over a period of years may chalk, checker, crack, blister, 
or shell off; the original colour of the paint may also change or even completely 
disappear. A high-class durable paint for outdoor use should wear well over four 
or five years, retain its colour, and chalk only to a moderate degree, so that on 
washing down a good surface remains for repainting. 

Paints which blister or crack are unsatisfactory, inasmuch as it is necessary 
to remove completely all the loose and badly adhering paint before any repainting 
can be done. 

In order to get a clear insight into the nature and properties of paints it is 
essential to have an accurate and clear knowledge of the physical and chemical 
properties of the components used in their preparation. 

The chemistry of the pigments will be found fully described in Part II. of 
this book, and that of the liquid mediums in Part ITI. 


CHAPTER II 


MANUFACTURE OF PAINTS 


PaINts are composed of :— 

(1) Pigments, 

(2) Oil or Oil Varnish Mediums, 

(3) Turpentine or other volatile spirits, 

(4) Driers, 
which are incorporated together in suitable proportions so that the resultant product 
may be easily applied and dry off with a hard and durable surface. The chief 
operations involved in the process of manufacture are pugging, grinding and mixing. 


PUGGING 


The pigments selected must be carefully tested to ensure that they are of 
uniform fineness and free from coarse particles; if there is any doubt about this 
they should be sieved through fine wire sieves in sifting machines specially made for 
the purpose. 

The pugging machine (Fig. 1) consists of a large, vertical, cylindrical iron vessel 
provided with a powerful stirrer fitted with blades and mechanically operated. 

The fine pigments are carefully weighed out and a portion emptied into the 
pug together with a little oil—usually raw linseed oil. 

The stirrer is set revolving, and gradually more and more pigment is added 
together with the oil until the whole is taken up, only sufficient oil being used 
as is necessary to convert the pigments into a very stiff paste. The amount of oil 
measured out and added to the pug is carefully noted. It is important to see that 
no more oil is used than is required to form a stiff paste. 

The pug is emptied by raising a slide at the bottom, the motion of the revolving 
blades forcing the pasty mass out into a pan placed in position to receive it. 


GRINDING 
(1) Rotter Mi1ts 


The paint paste is next ground through a triple roller mill (Fig. 2), which is 
now usually electrically driven. The roller grinding mills are made in various 
sizes, and the rolls may be made of either granite or chilled steel. 

The space between the rollers may be regulated at will so that any degree of 

a 


MANUFACTURE OF PAINTS 5 


fineness of grinding may be obtained. The middle roller has a lateral motion 
imparted to it whereby more efficient grinding is secured. 

The pasty material is introduced between the first two rollers, and a steel 
scraper takes off the ground material as it issues from the end roller. 

The paint is usually put through the mill two or three times, but where 
especially fine grinding is required it is necessary to put the material through 
the roller many times; towards the end 
of the operation the mill is screwed up 
very tightly so as to get the maximum 
grinding effect. 

Combination pug and roller mills are 
also made whereby the pugging and 
grinding operation can be carried out 
simultaneously. 










up 


\ 
\ 


caf 7 Aa aRS BY 


1 
oe 


(2) Epgz Runner MILLs il) 
a = 
Pigments may also be ground to paste At an toe 
form in edge runner mills in cases where i 





ell 
-! 

bszsszzed 

ey 








All <n 111119 


as, for example, in the manufacture of 
putty (whiting ground stiff in linseed oil) 
and paste driers. 

An edge runner mill (Fig. 3) consists 
of a circular basin-shaped iron trough which 
is fixed and on the bedof which the pigments 
and oil to be ground are placed. 

The grinding is done by means of a 
circular stone or steel runner set edgeways 
and fitted with gearing which causes it to 
run round the pan or bed of the mill. 

Many types of edge runner mills are 
made; the type in common use has two 
vertical runners provided with scrapers to Fie. 1.—Vertica Pua Mit. 

: : (Follows & Bate, Ltd.) 
prevent the material from caking on the 
bottom of the mill and to turn it constantly over so that effective mixing and 
grinding is obtained. 


a high degree of fineness is not essential, 




















Onn. 


(3) Firat Stone Grinpine Minus 


Flat stone grinding mills are extensively used for grinding pigments in water, 
and also in turpentine for making the so-called “ turps colours.” 

They are very slow, but grind extremely efficiently, and hence are still employed 
in the manufacture of gold-size colours for coach-work, and for colours in oil such 
as graining colours like siennas, umbers, Vandyke brown, etc., where an extremely 
fine product is required. 


6 THE CHEMISTRY OF PAINTS 


This type of mill consists simply of two-heavy circular flat stones placed on top 
of one another, the faces of which are cut into grooves so as to increase the grinding 
power of the stones. The lower stone is fixed, while the other is made to rotate 
over the other. The material to be ground is fed from a hopper through a circular 
hole cut in the upper stone, and passes as it is ground outwards to the edge and 
falls into a pan. 

The flat stones are usually made of granite ; French burr or other types of hard 
stones may be used. 

The Americans have introduced mills of this type in which the stones are replaced 
by grooved chilled steel and fitted with a cold-water cooling arrangement. 

These types of mills are very useful for grinding coach colours in oil or 
turpentine, as the cooling arrangement prevents any overheating which would 
cause discoloration or loss of turpentine by volatilisation. 


(4) Cont Mitxs 


Cone mills are largely used in the manufacture of enamels, and are very 
economical in use, as a battery of twelve or more of them can be worked by 
one man; further, only a moderate power is required to drive them. 

Cone mills may be arranged horizontally, but they are usually vertical. The 
grinding edges may be either of stone or, as is more usual, of steel, the grinding 
surface edge of which is deeply grooved (see Fig. 4). 

The mixture of pigments and varnish is emptied into the cone mill in a state 
of thin consistency, and the mill screwed up so as to regulate the flow of the ground 
liquid to ensure that the required degree of fineness of grinding is obtained. 

Usually the materials need to be run two or three times through the mill to 
obtain the necessary degree of fineness. The ground enamel is then sieved and is 
ready for use. 


MIXING MACHINERY 


The paste colours ground in oil are thinned down for use—that is to say, made 
into ready-mixed paints in paint-mixing machines. 

Various machines of this type are made, the simplest form of which consists 
of a pan into which can be lowered a paddle which is made to revolve at a moderate 
speed (see Fig. 5). 

The stiff ground paint is weighed out and introduced into the pan with a 
proportion of the paint medium. The paddle is then lowered into the pan and set 
revolving. 

As the paint mixes with the medium more and more of the latter is added till 
the paint is reduced to the right consistency, when it is run out through strainers 
and is ready for use. 

A full description of the special machinery used in the manufacture of paints 
is outside the scope of this book, and the reader who is desirous of such information 
is referred to the special works dealing with this subject (see Bibliography). 





Fic. 2.—TripLe Router Mintz. (Torrance & Sons.) 





Fig. 3.—Inon Epgt Runner Mrtz. (Torrance & Sons.) 


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CHAPTER III 


WHITE AND COLOURED PAINTS, ENAMELS, 
ANTI-CORROSIVE AND ANTI-FOULING PAINTS 


In this chapter a description is given of the various paints which are in common use 
for protective and decorative purposes, together with a general survey of their 
properties and the various purposes for which they are used. 


PASTE COLOURS 


Colours in oil are pigments ground to a pasty consistency in raw linseed oil 
which require thinning down with various paint mediums in order to make them 
ready for use. 

These paste colours may consist of genuine pigments—which is usually the case 
with the strong staining colours such as the umbers, ochres, siennas, etc.—or, as 
happens with the great majority of paste colours which are sold, of genuine pigments 
mixed with cheap inert bases or extenders, such as barytes, Paris white, and so on; 
such paste colours are sold as No. 1, 2 or 3 qualities, according to the amount of 
reduction. 3 

The amount of oil required to grind a pigment to a pasty condition varies to 
an enormous extent according to the specific gravity of the particular pigment. 
The white pigments, such as white lead, zinc oxide, etc., are ground in refined oil 
in order that discoloration of the pigment may be avoided. Usually a trace of 
ultramarine blue or Prussian blue is introduced during the grinding operation with 
a view to improving the colour of the finished product. 

Coloured paints, especially those made from the slow-drying pigments such as 
carbon black, purple oxides, etc., are ground with a proportion of boiled oil so as 
to improve their drying properties; a small amount of varnish or boiled oil foots 
is incorporated with the grinding oil in order that the pigments may grip the 
rollers better during the grinding operation, thus admitting of their being more 
finely ground and giving the finished product a smoother and more pleasing 
appearance. 

In the case of some of the paste colours it is customary to place a little water 
on the top of the casks in which they are stored to prevent skinning. Where the use 
of water would be objectionable oil paper should be used. 


7 


B 


8 THE CHEMISTRY OF PAINTS 


READY-MIXED PAINTS 


About fifty years ago the quantity of ready-mixed paints sold was comparatively 
small, the painter preferring to buy the paste colours and thin them down himself 
to the right consistency. In recent years, however, there has been an increasing 
demand for ready-mixed paints, and at the present time an enormous trade has 
sprung up in them. This is, no doubt, chiefly due to the labour saved in thinning 
down the paste colours, but also partly to the introduction of special paint mediums 
by firms engaged in the trade, whereby these paints are endowed with properties 
vastly superior to those of the product obtained by the painter with the ordinary 
mediums at his disposal. 

Paste colours are usually thinned down with an oil mixture consisting of four 
parts of boiled oil (pale boiled oil in the case of white and light-tinted colours) and 
one part of turpentine to the right working consistency, a small proportion of terebene 
or paste driers being stirred in to improve the drying properties of the paint. 

With many of the high-class ready-mixed proprietary paints special mediums 
are used, as has been mentioned above, for thinning the paste colours, as well as 
special machinery, so that a thorough incorporation of all the products takes place. 

The special mediums generally used by the paint manufacturer consist of a 
mixture of polymerised oils and elastic varnishes such as the copal varnishes, whereby 
special durable and hard-wearing properties are imparted to the finished paints. 

In recent years, owing to the high price of turpentine, various substitutes such 
as white spirits (see Chapter XVII.) have been used with satisfactory results, 
and it is quite likely, owing to the depletion of the American pine forests and 
the consequent increasing price of turpentine, that before long white spirit will 
eventually supersede the American spirits of turpentine as the volatile constituent 
in all ready-mixed paints. 

The paste and liquid driers employed in the manufacture of liquid paints to 
accelerate their drying qualities consist of the salts or oxides of lead cobalt and 
manganese, for a full description of which the reader is referred to the chapter on 
driers (Chapter XX.). 

The ready-mixed cheap paints so largely sold in small packages (1 and 2 Ib. 
tins) for amateur use are as a general rule of very poor quality on account of the 
large amount of weighting material such as barytes which they contain; for this 
reason they are usually coarse and deficient as regards body and covering power. 


ENAMEL PAINTS, ENAMELS OR JAPANS 


Enamel paints, especially white enamel paints, are exceedingly popular at 
the present time because of the beautiful, lustrous, highly-polished surfaces obtained 
by their use. 

These full-gloss paints are made by grinding the pure pigments extremely finely 
(zinc oxide usually in the case of white enamels) in the requisite quantity of a 
mixture of stand oil and copal varnish. 


WHITE AND COLOURED PAINTS, ETC. 9 


As a rule enamels dry rather slowly, especially those made with a large amount 
of stand oil, requiring sometimes as long as twelve to eighteen hours before they are 
surface dry. ‘They possess excellent body and covering power, and as a consequence 
of their tough and elastic nature are exceedingly durable, wear well, and retain their 
gloss for a long period under the severest exposure tests. 

White enamels are sometimes made by grinding zinc oxide in pale dammar 
varnish ; the enamel so made is extremely white in colour, but owing to its brittle 
nature is suitable only for indoor use. 

No definite proportions can be given for the amount of oil varnish mixture 
required to a given weight of pigment, as this naturally varies considerably according 
to the nature of the pigment or pigments used in its manufacture. 

Flat Enamels—Enamels may also be manufactured so that they dry with a 
flat or matt finish; sometimes with a half-gloss or egg-shell finish, according to 
the purpose for which they are intended. 

Flat or half-gloss enamels are made in exactly the same way as the full-gloss 
enamels, but the proportion of the varnish used to pigment is decreased whilst the 
amount of turpentine is increased. Sometimes a proportion of wax may be added 
so as to produce the desired flatting result. 

Flatted enamels are largely used as flat wall finishes and for general indoor 
decoration, and for this purpose they are much superior to distempers (see 
Chapter IV.) on account of the permanency and beauty of finish which characterise 
them. “Further, they can be easily washed down when required without in any way 
spoiling the beauty of the surface of the enamel. These paints are usually “ stippled ” 
with the object of imparting to them a soft velvet finish. On account of the 
comparatively small amount of varnish used in their preparation they are not 
suitable for outdoor use unless protected with a coat of varnish. 

Quick-drying Varnish Paints and Enamels, Petrifying Liquids.—Quick-drying 
varnish paints are usually prepared by grinding the pigments in sharp-drying rosin 
or oil rosin varnishes. They dry off as a rule in an hour or two with a glossy surface. 

These varnish paints are generally a cheap line of goods, and are only suitable 
for painting toys, furniture and such like, and for internal work generally, for owing 
to their rosin content they soon become brittle and crack and shell off when exposed 
to weathering influences. 

Care should be taken to use only those pigments which do not thicken up or 
liver (“‘ feed up’) with rosin varnishes, otherwise the paints would quickly set up 
solid in the containers and be rendered unfit for use. 

Speaking broadly, hardened rosin varnishes are used in their preparation—that 
is to say, varnishes in which the rosin acids have been neutralised by zinc oxide or 
lime (see Chapter XVIII.). White petrifying liquids, for example, are often made 
by dissolving up rosin in white spirit or naphtha and running the hot solution on to 
zinc oxide, ground to a paste in linseed oil, and stirring well. Vigorous action takes 
place, due to the combination of a portion of the zinc oxide with the rosin, and when 
the reaction is over the white petrifying enamel is run through sieves into containers 
and is ready for use. 


10 THE CHEMISTRY OF PAINTS 


Petrifying liquids, whether coloured or transparent, for outdoor use require 
to be made from copal varnishes to withstand the severe weathering conditions 
to which they are liable to be exposed. 

Gold-size Colowrs.—Colours bound in gold size are pigments which have been 
ground to a paste form in quick-drying gold size, e.g. shellac gold size; they are 
extensively used by coach painters as body colours. They dry off very quickly, 
giving hard flat surfaces which can be easily rubbed down and over which varnishes 
are applied so as to get the desired finish. 

In the manufacture of gold-size colours only pure pigments or lakes should 
be used, and it is essential that the grinding should be as near perfection as possible. 

For many purposes the pigments are ground in turpentine (turpentine colours), 
a little gold size being afterwards added by the painter to produce the desired 
binding effect. 


AGRICULTURAL AND IMPLEMENT PAINTS, DIPPING AND 
SPRAYING PAINTS 


Paints used for agricultural machinery, etc., may be quick-drying gold-size 
colours which require varnishing ; but as a general rule it is found more convenient 
to use enamel paints which are made of hard-wearing copal varnishes ; these dry off 
with glossy surfaces, wear well, and retain their colour and gloss under all weathering 
conditions. They are usually supplied to the manufacturers of agricultural 
machinery in a thin liquid condition so that they may be applied by spraying or 
by the dipping process. 

The dipping and spraying processes have come rapidly into favour in recent 
years owing to the rapidity and ease with which they can be used, and the great 
saving of labour effected in applying paints and varnishes as compared with the 
brush method. 


STAINING AND GRAINING COLOURS 


Strong staining colours consisting of such pigments as siennas, umbers, Van- 
dyke brown, yellow ochre, and so on, ground to a paste form in linseed oil, are 
extensively used by painters for obtaining the various tints required in their work. 

By the skilful use of these colours the expert painter is enabled to produce 
remarkably good imitations of mahogany, oak, walnut, etc., out of ordinary 
white wood. 

The processes of glazing and scumbling, in which one colour is superimposed 
on another, permits the experienced artist to produce those beautiful effects that 
are familiar to all. 


ANTI-CORROSION PAINTS 


The protection of ironwork from corrosion by means of specially prepared 
paints has occupied the attention of paint chemists for many years, and an immense 
number of experimental practical trials has been carried out at various times in an 
endeavour to elucidate this very important problem. 


WHITE AND COLOURED PAINTS, ETC. 11 


Sir Robert Hadfield has estimated that the annual loss caused by the corrosion 
of iron and steel amounts to no less a figure than twenty-nine million tons. 

Various bitumen preparations made from asphaltum, coal tar pitch, etc., in 
conjunction with a proportion of boiled oil—such as the well-known Dr Angus Smith’s 
bitumastic composition—have been in use now for many years, and have been found 
to give most excellent results. 

It has also been found, after a long series of practical trials (many of which have 
been carried out in America), that those pigments which inhibit corrosion may be 
divided into two classes, viz., those which are alkaline or basic, and those which 
comprise the chromates, the latter group owing its value in this respect to the well- 
known power of chromic acid to act on nascent hydrogen and to induce the “ passive 
state ”’ in iron. 

The pigment in most general use as a priming or first coat for iron structures 
such as bridges is red lead, which is a basic pigment possessing anti-corrosive pro- 
perties which are beyond dispute. 

Red lead when mixed in oil, as is common knowledge, tends to set up hard, 
and for this reason requires to be used soon after mixing. Recently, however, brands 
of red lead (free from litharge) have been placed on the market which are non-setting 
and which may be mixed in oil and kept an indefinite time without undergoing any 
perceptible thickening or setting up. 

Graphite and ferri-silicon paints have also been found to have excellent anti- 
corrosive properties, and are largely used for painting ironwork. 

The medium used with such pigments as red lead, graphite, etc., is most 
commonly boiled oil, though it has been found that the addition of polymerised 
oils such as stand oils and treated wood oils (see Chapter XVI.) to the boiled oil 
tends to prolong the life of the paint and also at the same time to cause the paint 
films to be more impervious to moisture. 

Paints made from lead and zinc chromes have also been found by practical tests 
to possess excellent anti-corrosive qualities, though their general use for this purpose 
has, on account of their comparative costliness, not been adopted to any great extent. 

Red oxide of iron paints, as well as paints made from black oxide of iron and 
carbon black, are, by reason of their cheapness and first-rate anti-corrosive properties, 
very largely employed for the protection of iron and wood surfaces, and on the 
whole with very satisfactory results. 

Anti-corrosion paints that are used as a protective and first coating on ships’ 
bottoms are usually made from a strong oxide of iron (containing not less than 
80 per cent. Fe,O,) ground in a quick-drying oil dammar varnish, and thinned out 
with low flash shale naphtha. 


ANTI-FOULING COMPOSITIONS 


Anti-fouling paints are used on ships’ bottoms in order to prevent the growth 
of barnacles and weeds. 
They are as a general rule quick-drying iron oxide paints to which a proportion 


12 THE CHEMISTRY OF PAINTS 


of poisonous material has been added, the amount of poisonous substance being 
greater in the case of ships sailing in tropical waters, where of course the growth 
of weeds and barnacles is much more rapid than in the colder regions. 

The poisonous materials used are white arsenic, mercury oxide, finely 
precipitated sub-oxide of copper (Cu,O), copper sulphocyanide, emerald green, 
copper sulphate, Scheele’s green, verdigris, etc. 

The medium used in their preparation is a gum oil varnish, containing a 
proportion of rosin and thinned down with shale naphtha so that the paints will 
dry off rapidly and thus allow the painting work to be expeditiously carried out. 

Anti-fouling compositions are sometimes made by mixing the poisonous material 
with a wax basis, which requires to be melted and “ clagged” on hot by the aid of 
trowels. 

In painting a ship’s bottom two coats of anti-corrosive priming and one coat 
of anti-fouling composition are applied. The majority of anti-fouling compositions 
are of a dark red colour, but occasionally green anti-fouling compositions are met 
with, the colouring matter in this case being a mixture of emerald and mineral green. 

The following analysis by the author of some of the well-known anti-fouling 
compositions which are in common use will give a general idea of the composition 
of these paints :— 


(1) For Tropica WatTErs 


Pigment . ; t ; ‘ 4 . 43-10 per cent. 

Oil, resin mixture. : : : .. 80-20 is 

Shale spirit ant ; ; : . 26:70 Fe 
100-00 





The oil and gum mixture contained 8 per cent. of free rosin. The resinates 
consisted of equal parts of zinc and copper resinate. 


Analysis of Pigment 

Ferric oxide (Fe,O3) . : ‘ : . 22-54 per cent. 
Sub-oxide of copper (Cu,0) : , . 34:20 i 
Copper sulphocyanide (CuCnS) . ; . 14-41 Ee 
Mercury oxide (HgO) ; 4 ‘ my Loe es 
White arsenic (As,O3) : : ; fa o00 2 
Lime (CaO) : ; : . . ~~ 2-06 a 
Zinc oxide (ZnO) : : : : <a G6 oh 
Sulphur trioxide (SO,) : ‘ : Rees Wo) si 
Sodium sulphate (Na,SQ,) . ; 3 2 PELSOG is 
Insoluble matter ; : ; ‘ a 50 le 
Moisture and alkalies 5 : ; meets i) 





100-00 





WHITE AND COLOURED PAINTS, ETC. 13 





(2) Pigment . : é : ; : . 42-70 per cent. 
Oil, gum resinate : ‘ , ; . 29-10 35 
Shale naphtha . : ‘ . 28-20 i 

100-00 





The oil, gum resinate was of a greenish colour and an analysis of the ash gave— 


Copper oxide (CuO) . . 4-01 per cent. 
Zinc oxide (ZnO) : : é > 2°00 dp 


Analysis of Pigment 





Sub-oxide of copper (Cu,0) F : . 932-58 per cent. 
Ferric oxide (Fe,O3) . : . 34-10 - 
Oxide of mercury (HgO) . , 7 yh ia y | if 
Calcium sulphate (CaSO,) . : ‘ A elie . 
Silica (Si0,) . : : : ae!) “s 
Magnesium oxide (MgO) at ih ek te Fe 
Calcium chloride Oi tone : : Paes Sea a 
Moisture . ? : : ; 1850 a4 
100-00 





(3) Comp Water ANTI-FOULING COMPOSITIONS 





Pigment . : : ; : : . 36°31 per cent. 

Rosin, ete. : : ; ° E . 36-90 a 

Shale spirit . : : : ; BV ie 
100-00 





The varnish residue contains 73 per cent. of free rosin, the remainder being calcium 
resinate. The resinates contain 6 per cent. of arsenic. 


Analysis of Pigment 


Ferric oxide (Fe,05) . : . p . 56-00 per cent. 
White arsenic (As,05) . : : pen 21-16 ue 
Zinc oxide (ZnO) : : ? : i e2l-O1 BS 
Mercury oxide (HgO) , ; : Pole BS pal piss 
Calcium sulphate (CaSO,) . : : . 12-25 3 
Silica (Si0,) .. 1 ; : : tome 270 i 





100-00 





14 THE CHEMISTRY OF PAINTS 





(4) Pigment . : : ; ‘ , . 26-50 per cent. 
Shale spirit : ‘ ; ; : . 2510 
Resinates : : 2 : ; . 48-40 + 

100-00 





The resinates consist chiefly of zinc resinate. 


Analysis of Pagment 





Silica (Si0,) : ‘ 4 ‘ . 4-76 per cent. 
Ferric oxide (Fe,O3) . ; ; 4 . 930-46 Hs 
Zinc oxide (ZnO) ‘ ; , : » 2000 . 
Copper Sulphate (CuSO,) . : : 1S a 
White arsenic (As,O3) ; : , See Us . 
Mercuric oxide (HgO) ; : : . 639 a 
Calcium sulphate (CaSO,) . : : . ee > 
100-00 





As an immense variety of paint products are manufactured for different industrial 
uses, both in the paste and the ready-mixed form, it would be quite impossible, as 
will be readily understood, to give a detailed description of them all with their 
diverse properties, but it is hoped that the description given above will indicate in 
general outline the methods in vogue for their preparation, as well as their 
composition. . 

It will of course be understood that paints used in the neighbourhood of gas 
works and acid works require to be made with pigments which are unaffected by 
sulphuretted hydrogen (which precludes the use of white lead) and acid fumes, and 
also that the mediums in which the pigments are ground should on drying give 
tough and impervious films highly resistant to all chemical agencies. 

White paints made for hot-houses should be made on a zinc oxide basis, as 
white lead paints are often found to develop rose-coloured spots over their surface, 
due to the growth of a paint-destroying fungus. 

As the appearance of these red spots has often been a source of mystification 
even to experienced paint technologists, the following interesting account, taken from 
Gardner’s “ Paint Researches and their Practical Application ” (Washington, D.C., 
pp. 276-7), may be cited as throwing valuable light on the subject :— 


“Among the most remarkable of fungi is one that elects to grow on fresh 
paint. It flourishes in the greatest profusion in hot-houses, its development being 
apparently favoured by a high temperature and constant humidity, as it is but 
rarely observed on paint elsewhere. About a month or two after a hot-house has 
been painted, more especially if white paint has been used, numerous small, rose- 
coloured specks appear on the paint; these specks gradually increase in size and 
change to a purple or sometimes dark red colour, suggesting the idea of blood 


WHITE AND COLOURED PAINTS, ETC. 15 


having been spread over the paint. In course of time the discoloured areas extend 
considerably and form broadly-effused patches several inches across. About a week 
after the coloured patches are fully developed their surface becomes studded with 
minute blackish-red warts. Hach wart is a fungous fruit, containing myriads of 
very minute spores, which in due course are dispersed and start new points of 
infection. 

“‘ When the spores of the fungus are sown on a streak of wet white paint, a faint 
roseate tint appears in about a week’s time, and within three weeks fruit is produced 
in abundance, and the deep purple characteristic blotches are well developed. 
Spores sown on a thin smear of pure linseed oil germinate as readily as in paint, 
but the mycelium remains colourless, and so far, no fruit has been produced. The 
result is the same when the spores germinate in ordinary nutritive media or in water. 
No germination takes place when the spores are sown on a streak of pure white lead 
or carbonate of lead (pigment). Hence this substance alone is not a suitable medium 
for the growth of the fungus, although its presence is necessary to enable the paint 
to complete its normal course of development, and it is also the constituent from 
which the fungus produces as a by-product the purple-red colouring matter which 
is collected in oily-looking drops within the cells of the mycelium, the cell walls 
themselves remaining colourless. The red colour suggests that the white carbonate 
of lead undergoes some chemical change induced by the presence of the fungus, 
resulting in the formation of red oxide of lead. This matter, however, requires 
careful investigation. The presence of 2 per cent. of carbolic acid in paint 
completely arrests the development of the fungus.” 


METALLIC PAINTS 


Metallic paints, such as aluminium and gold paints, are extensively used on 
account of their anti-corrosive and highly decorative properties. They are prepared 
by simply mixing the finely powdered metals or their alloys with suitable varnish 
mediums. 

The metals must be in an exceedingly fine state of subdivision, and are manu- 
factured by special processes involving the use of intricate grinding machinery. 

The mediums used may be either thin copal varnishes or celluloid varnishes, 
the latter being preferable on account of their neutral and colourless properties. 

Aluminium paints are made by stirring in about 3 lbs. of the fine metallic 
powder—as free from grease as possible—into 1 gallon of the medium and 
mixing well. 

Gold paints are made in the same way as aluminium paints, various shades 
being obtained according to the particular colour of the gold or bronze powder 
used. 

Various coloured effects may also be obtained by mixing different coloured 
aniline dyestufis with the metallic paints, giving us green, blue, yellow, etc., coloured 
metallic paints. 

As the gold and bronze powders have a much greater specific gravity than 


16 THE CHEMISTRY OF PAINTS 


that of aluminium, much more of them will be required to the gallon of medium, 
roughly about 6 lbs. to the gallon being necessary. 

Since copal varnishes ordinarily contain acids from the copal gums used in 
their manufacture, care must be taken to neutralise them with lime, zinc, oxide, etc., 
before use as metallic paint mediums, otherwise they would act on the metallic 
powders ; turning them green in the case of the gold powders and thus spoiling the 
colour of the paint; whilst in the case of aluminium powders hydrogen may be 
evolved. 


LUMINOUS PAINTS 


The commercial sulphides of calcium, barium and strontium possess the 
properties of appearing luminous (“ phosphoresce”) in the dark, after being 
previously exposed to light, and are used in the manufacture of luminous paints. 
The light emitted gradually diminishes in intensity, but on re-exposing the com- 
pound to the light, its luminosity is restored. 

This singular property has been long known, and calcium sulphide (CaS) was 
formerly termed “ Cantous phosphorus,” and barium sulphide (BaS) “ Bononian ” 
(7.e. Bolognian) phosphorus. 

Balmain’s luminous paint, which is the best known of these products, is a 
sulphurous combination of calctum made by the aid of a high degree of heat. 

The pure sulphides do not phosphoresce, so that this property would appear 
to be attributable to the presence of minute quantities of foreign substances. 
Traces of other elements, such as bismuth, cadmium, manganese, etc., modify the 
colour of the phosphorescent glow. 

These alkaline earth sulphides are converted into paint form by mixing with 
gum arabic solution or a gum dammar varnish medium. Acidic varnishes such 
as copal varnishes containing lead driers cannot be used, as they would destroy the 
sulphides. 

Radio-active luminous paints, which are used for painting watches, compasses, 
etc., differ from the formerly known phosphorescent substances in the fact that 
they do not require any prior exposure to light. On the contrary the action is in 
this case produced permanently by the rays which are thrown off by the radio- 
active substances such as mesothorium and radiothorium used in their preparation. 


CHAPTER IV 


DISTEMPERS, COLD WATER PAINTS 


WasuHaBLE Distempers, or cold water paints, are in great demand at the present 
time on account of their comparative cheapness, and also because of the large range of 
shades in which they are made and the beauty of the matt finish obtained by their aid. 

Washable distempers are manufactured either in the form of a thick paste or 
jelly, or in powder form. 


DRY DISTEMPERS 


These distempers (called Kalsomines in America) are sold in two forms—those 
which require to be mixed with hot water to develop their adhesive properties, and 
those which are prepared for use simply by the addition of cold water. 

Cold water distempers usually contain casein as the binding agent in association 
with alkalies or alkaline earths. On the addition of cold water the alkali is dissolved 
and acts as a solvent for the casein. 

Sometimes dextrine, or finely powdered glue which has been previously treated 
so as to render it soluble with cold water, may be used in place of casein. 

The coatings furnished by these casein distempers dry quickly, giving matt or 
flat surfaces which, after a few days’ exposure to the air, become insoluble and 
adhere so firmly that they may be lightly sponged over without washing off. On 
account of the firmness of the adhesion and insolubility of these paints it is possible 
to apply a second coat of distemper a few hours after the first coat has dried, a 
property which is very valuable in cases where two or three coats are necessary 
in order to completely hide the surface which is being painted. 

These paint surfaces are usually stippled so as to hide all brush marks that 
might otherwise be in evidence, and also to give the surface a matt velvet-like finish. 

In addition to the binding constituents, these paint powders contain one or 
more of the following materials: whiting, China clay, terra alba, lime, etc., together 
with the necessary tinting colours. 

Whiting is undoubtedly the best white base for distempers, as it possesses 
excellent body and whiteness in water (oil, on the other hand, turns it a dirty trans- 
parent grey colour), and is superior in this respect to either terra alba or China clay, 
which are much more transparent. As a rule, however, a proportion of China 
clay or terra alba is used in conjunction with the whiting in order to improve the 
flowing power and ease of application of the finished paint. 

17 


18 THE CHEMISTRY OF PAINTS 


The pigments used for tinting the distempers must be permanent and perfectly 
fast to lime and alkalies. Consequently such colours as Prussian blue, vermilionettes, 
lead chromes, cannot be used, and in their place pigments such as ultramarine blue 
(also alum-resisting), Lithol red, Hansa yellow, etc., must be substituted. 

In hot water dry distempers the binding agent is powdered glue or size. In 
this case no alkali is necessary, as the size readily dissolves on the addition of hot 
water. 

Size distempers are, generally speaking, not so washable as those made with 
casein, so that on applying a second coat there is a tendency for it to work up the 
under coat, which spoils the finished surface of the paint. To avoid this trouble it 
is customary to add a small proportion of some hardening agent, such as bichromate 
of potash, formaldehyde, stearate of lime, alum, etc., so that the paint surfaces 
on exposure to air and light dry off with more or less insoluble films or surfaces. 

The pigment used in the tinting of distempers should always be first tested in 
lime and dilute alkaline solutions to see that they are quite permanent to these 
agents, otherwise the distemper may be rendered useless. This is especially 
desirable in the case of many of the lime greens which are sold as being fast to 
lime, but are found on testing, even after only a few days’ exposure, to completely 
fade away. 

Dry cold water paints are manufactured by grinding the colours, etc., in an 
edge runner and adding the casein, or glue binder, in sufficient quantity to fix properly 
the pigment and bases used. Great care must be taken to see that all the materials 
used are thoroughly dry before being incorporated together, as even a small portion 
of moisture present would cause the powder to cake and set up into hard lumps, 
’ and, of course, render it useless. 

A little boric acid, salicylic acid, aluminium sulphate or other dry preservative 
is added to keep the dry powder sweet and prevent any decomposition that might 
take place on standing. 

The powder should be ground very finely and sifted through special sifting 
machinery in order to get the necessary sub-division of the particles and their 
intimate admixture (see Fig. 6). 

The dry distempers are then packed in waterproof containers, and should be 
stored in a dry place, as in a moist atmosphere rapid deterioration would take place. 


PASTE DISTEMPERS 


These are manufactured by grinding together pigments such as lithopone, zine 
oxide, Paris white, blanc-fixé, etc., in a special medium which on cooling sets to 
a jelly-like consistency. These paste distemper grinding mediums are made by 
dissolving glue in hot water and thoroughly incorporating a proportion of linseed 
oil or a wood oil varnish till an emulsion is formed. 

A small percentage of liquid carbolic acid, boric acid or formaldehyde is added 
as a preservative to keep the distemper sweet, otherwise on storage it would go — 
mouldy and decompose. 


ao 
i Kt il 





Fic. 4.—Cont Paint MILL. Fig. 5.—Liqurip Parnt MIXER. 
(Follows & Bate, Ltd.) (Torrance & Sons.) 













4 


hii 


= 








Fic. 6.—GarpNER’s CoMBINED Rapip SIFTER AND MIXER. 





DISTEMPERS, COLD WATER PAINTS 19 


Sometimes casein dissolved in alkaline solution is used in place of the glue as 
the binding agent. 

The pigments used to tint these distempers must be fast to lime, as in the case 
of the powder distempers. 

Paste distempers are made ready for use simply by adding sufficient hot water 
to reduce them to a creamy consistency. The pigment content of white paste 
distempers usually contains 30 per cent. of lithopone and 70 per cent. of Paris white, 
which is ground in a 10 per cent. solution of glue containing about 15 per cent. of 
oil or varnish mixed with it. A little ultramarine blue is added to increase the 
whiteness of the finished product. 

A little alum may be used to act as a hardening agent, and sometime Irish moss 
is mixed with the glue solution in order to improve the brushing and laying-on 
properties. 

The bright red distempers are prepared from aniline lake pigments fast to lime, 
such as Para or Lithol red precipitated on Paris white, whilst the greens are made 
from basic aniline dye-stufis such as brilliant green or malachite green on green 
earth. The yellow pigments used may be either ochres, zinc chromes, or Hansa 
yellow struck on Paris white. Other tints may be obtained by the use of ultra- 
marine blue, siennas, umbers, Venetian reds, and so on. 

The following recipes (taken from Scherer) will give the reader a general idea 
as to the composition of these distempers made with casein as the binding agent. 


(1) Dry White Distemper. (2) Dry Stone Distemper. 
Parts by Weight. Parts. 
Casein, soluble in alkali. . 100 10 
Caustic lime from marble . . 100 10 
Levigated chalk oe 2 800 40 
Borax. ; ; il 1 
Ultramarine. ‘ ‘ 2 to 23 Ochre 40 
(8) White Paste Distemper. (4) Coloured Dry Distempers. 
Parts by Weight. Parts by Weight. 
Casein. ; , . 144 Casein : j See. ti 
Slaked lime . ; ‘ 7 Powdered slaked lane ; . 20 
Spanish white . : - 200 Kaolin ‘ : . 150 
Water. ; : 7 20 Whiting . : . 800 


Lime fast niente accord- 
ing to colour desired 5 to 20 


PROPERTIES AND UssEs oF DISTEMPERS 


Distempers should readily thin down to suitable brush consistency on the 
addition of the necessary amount of water. They should possess good body and 
covering power, and brush on easily without any pull. On drying off, the surface 


20 THE CHEMISTRY OF PAINTS 


should show no signs of streakiness or brush marks and should be a perfectly flat 
finish. 

The tints should be permanent and the ready-mixed distemper should be free 
from any offensive odour, and should retain its sweetness even after it has been mixed 
for several days. 

The distemper should second coat soon after the first coat has dried on without 
working up or in any way interfering with the first coat. The finished distemper 
when dry should adhere firmly to the surface to which it is applied and not scale 
or rub off ; it should also withstand washing with water. 

Distempers are often used in place of oil paints as a cheap priming paint on 
wood, plaster and stone surfaces in order to lessen the cost; the resulting smooth 
level surface thus obtained lends itself admirably to the subsequent application 
of oil paints. 

As has already been stated, distempers are very largely used as a cheap flat 
wall paint in place of wall paper, and are extremely popular on account of their 
sanitary properties and the beautiful matt effects which may be obtained by the 
judicious use of the many tints which are available. 


ANALYSIS OF DISTEMPERS 


The analysis of a distemper is a comparatively simple matter; as a rule a 
simple qualitative analysis being all that is necessary. The base, which usually 
consists of one or more of the following materials—Paris white, China clay, terra 
alba, zinc oxide and lithopone, together with the necessary tinting colours—may 
be determined by the usual analytical methods. 

The percentage of casein or glue used as the binding agent may be estimated 
by making a nitrogen determination by the well-known Kjeldahl method. The 
presence of an alkali will indicate that casein has been used in its manufacture ; 
if absent it may pretty generally be inferred that glue is the binding agent. 


FIREPROOF PAINTS 


Paints manufactured as a protective coating to wooden structures in order to 
render them fireproof may be divided into two classes—first, those that have an oil 
vehicle, and secondly, those made with a distemper medium. 

The base usually employed is finely powdered asbestos, which is tinted with the 
necessary pigments which must be impervious to heat. A small proportion of 
chemical salts, such as alum, tungstate of soda, ammonium phosphate, etc., which 
possess the property of preventing inflammability are also ground into the paint. 

A medium made up with silicate of soda solution and casein possesses valuable 
fireproof properties and is superior in this respect to those mediums made up from 
either oils or a glue solution. 

A first coating or priming solution, consisting of an aqueous solution of sulphate 
of alumina or ammonium sulphate, is usually first applied to the wood and allowed 
to soak in and dry before applying the subsequent coats of fireproof paint. 


CHAPTER V 


THE ANALYSIS AND VALUATION OF PAINTS 
AND ENAMELS 


THE analysis of paints and enamels as regards their chemical composition and 
physical properties is a matter of the utmost importance, as it is only by means 
of a very careful and systematic examination of these products that an accurate 
estimation of their value can be deduced. 


CHEMICAL ANALYSIS 


Separation of the Vehicle—JIn the chemical analysis of a paint it is necessary 
first of all to separate the vehicle from the pigment. This may be done by 
extracting the vehicle in a Soxhlet’s (Fig. 7) or other convenient extraction 
apparatus, using either acetone or other suitable solvent as the extracting agent. 

A very easy and convenient method of separating the medium from a paint 
so as to obtain the dry pigment consists in weighing out about 5-10 grams of the 
sample in a tall narrow beaker and adding 50 c.c. of petroleum ether, stirring well 
and leaving a few hours to settle. The top clear liquid is then decanted off through 
a double weighed filter paper into a weighed conical flask. The extraction process 
is repeated three or four times, and in the last one, acetone or benzol may be used 
in place of the petroleum ether in order to obtain a more perfect extraction. The 
pigments are then washed on to the filter paper, dried and weighed. 

The amount of oil or oil varnish is obtained by distilling off the solvent 
extract and weighing the residue. 

Another very convenient method for separating the vehicle from the eto: 
is by centrifuging the paint in a centrifugal machine. 

The amount of the volatile constituent in a ready-mixed paint is estimated 
by distilling off 100 grams or more of the sample and collecting the distillate, or 
(more roughly) by heating on a sand bath and weighing the residue after all the 
volatile matter has been driven off. 


ANALYSIS OF THE PAINT VEHICLE 


The paint vehicle may be either a mixture of raw and boiled oils thinned with 
turpentine, white spirit, naphtha, or other volatile solvent, or it may consist of a 
21 


22 THE CHEMISTRY OF PAINTS 


rosin or a gum varnish, or mixtures of both, with or without the addition of 
linseed oil. 

The nature of the separated medium in which the pigments were ground 
may be readily ascertained by pouring a few drops of it on to a sheet of glass and 
examining the film obtained on drying. A mixture 
of raw and boiled linseed oils will give a softish 
film which dries in about twelve hours, whilst a 
rosin or oil varnish will dry more rapidly, giving 


i) 
(IMT 












(TC P| 





Fic. 7.—SoxuHuLEt’s EXTRACTION 


APPARATUS. 


jp la 
Ls &y 


“eg 


5 oa 





tough and highly lustrous films, due to their resin 
or rosin content. 

The presence of rosin in the vehicle may be 
determined by the Lieberman-Storch test for rosin 
(see page 162). 

If the vehicle consists of linseed oil, its freedom 
from mineral oil may be ascertained by adding three 
drops to an alcoholic potash solution, boiling well, 
and then adding distilled water. The solution 
should remain perfectly clear, any turbidity indicat- 
ing the presence of unsaponifiable matter (mineral oil). 

If the medium consists only of linseed oil (or 
other drying oils) a determination of its specific 
gravity, lodine value, etc., may be carried out 
according to the usual procedure for the analysis of 
oils (see Chapter XVI.) in order to determine its 
exact composition. 

If rosin varnishes or gum varnishes are present 
then the nature and the amount of resin and oil 
present may be estimated by the ordinary methods 
adopted for the analysis of oil varnishes (see Chapter 
XVIII). 

The volatile constituents driven off are usually 
turpentine or white spirit, and should be fractionated 
in order to decide their composition, though as a 
general rule the smell will suffice to give a good idea 
respecting their nature. 

A portion of the vehicle should be burnt off 
and the residue examined in order to determine the 


amount and nature of the soluble driers that have been used in its preparation 


(see Chapter XX.). 


ANALYSIS OF THE PIGMENTS 


The dry pigment or pigments obtained after the removal of the vehicle 
should first of all be qualitatively analysed with a view to deciding their nature 


ANALYSIS OF PAINTS AND ENAMELS 23 


and the approximate quantities present. By this preliminary analysis much time 
will be subsequently saved when the quantitative estimation is carried out, as the 
analyst will then be in a position to draw up a scheme of analysis suitable for the 
particular dry material under examination. 

The quantitative analysis of the pigments separated from a paint offers no 
particular difficulties, and is carried out according to the usual schemes of analysis, 
descriptions of which will be found under the various chapters devoted to the 
chemistry of the different pigments commonly used in the manufacture of paints. 


WHITE PAINTS 


The pigments used in the manufacture of white paints are usually white lead, 
zinc oxide and lithopone, though occasionally white oxide of antimony and titanium 
oxide may be met with. 

These pigments may be used alone, or mixed together in suitable proportions 
in the pure state; but as a general rule they are associated with inert bases ore 
extenders such as barytes, Paris white, terra alba, silica and china clay, which are 
added in various proportions to reduce the cost of the paint. 


COLOURED PAINTS 


The composition of coloured paints is a much more complicated matter than 
that of the white paints on account of the large range of pigments that may be 
used in their preparation; also on account of the fact that the same or nearly 
the same coloured paints may often be produced by entirely different combinations 
‘of colour pigment. 

A brief indication of the colour pigments present in the more commonly used 
coloured paints will give a general idea of the composition of the latter. It will, 
of course, be understood that besides these colour pigments it is usual to add as 
extenders, in order to reduce the cost of the paint, inert bases such as barytes, 
Paris white, etc. 

Black Paints—Carbon black, vegetable black, black oxide of iron, ivory black, 
lamp black, graphite. 

Red Oxide Paints—Red oxide of iron, Venetian red, Tuscan red, Turkey red 
oxide, Indian red. 

Bright Red Paimts——Vermilion, vermilionettes, para red, alizarine lakes, lithol 
red, helio fast red, and other aniline red dye-stuffs precipitated on suitable bases. 

Blue Paints Ultramarine, Prussian blue, Brunswick blue, cobalt blue, aniline 
blues (Methylene Blue Lake, etc.). 

Yellow Paints——tLead chrome yellow, zinc chrome, ochres, aniline yellow lakes 
such as Hansa yellow, lithol yellow, etc. 

Green Paints—Brunswick greens, green oxide of chromium, zinc greens. 
Also aniline greens such as malachite green, brilliant green, etc., precipitated on 
a green earth or other base. | 

Brown Paints —Umber, Vandyke brown. 

c 


24 THE CHEMISTRY OF PAINTS 


Purple Oxide Paints.—Purple oxide of iron. 

The various tinted paints which are obtained by the addition of small amounts 
of different pigments to a white base such as white lead or zinc oxide are innumer- 
able, and no useful purpose would be served by attempting to enumerate them. 
The reader who is interested in the subject is referred to the special works dealing 
with the subject of Paint and Colour Mixing (see Bibliography). 


ESTIMATION OF WATER IN PAINTS 


Ready-mixed paints usually contain a small proportion of water in order to 
prevent the pigments present from settling out hard in the containers on long 
standing. The amount of water used varies from 1 to 3 per cent., and so long as 
this proportion is not exceeded its addition is beneficial inasmuch as ready-mixed 
paints, especially those which are exported, are often packed for months or even 
years before they are used. If water were not added the paint would set to a 
*hard mass at the bottom of the containers and be rendered practically useless. 7 

Some manufacturers employ various patent emulsifying agents in place of 
water such as glue solutions, solutions of common salt, soda carbonate, sugar of 
lead and the like. 

Whiting, China clay, and blanc-fixé (precipitated barytes) are often used in 
place of ordinary barytes with the heavier pigments on account of their non-settling 
properties, which helps to keep the pigments in suspension and prevent them 
settling out hard in the containers. 

The addition of a small percentage of glycerine has also been found to be very 
useful in preventing settling in ready-mixed paints, as also the “ livering”’ of certain 
pigments, e.g. Prussian blue when ground in oil. 

The presence of water in a paint may be detected by rubbing it on a white 
porcelain slab with a little eosin dye-stuff. If water is present the eosin will be 
turned a pinkish colour, otherwise no change will be apparent. 


PHYSICAL TESTS 


The quantitative analysis of a paint will give very valuable information as 
to the nature and quantity of the pigments and vehicle which have been used in 
its preparation, but this requires to be supplemented by a series of thorough, 
practical tests if we are to gain an insight into its value as a protective coating for 
the various purposes for which it is to be used. 

The value of a paint is judged according to the following properties :— 


(1) Fineness. 

(2) Consistency and working qualities. 

(3) Body. 

(4) Covering power. 

(5) Time of drying. 

(6) Nature of the dry surface; its durability and wearing properties. 


ANALYSIS OF PAINTS AND ENAMELS 25 


The practical testing out of the paint should be carried out in the following 
manner :— 

A series of pink primed boards about 30 inches long and 12 inches in width 
are prepared by giving them two coats of a hard drying pink priming paint and 
rubbing down well after each coat. 

The paints to be tested are stirred well up so as to get a thorough admixture 
of all the ingredients, and applied with a clean brush, care being taken to lay on 
the paint evenly, and remembering that two thin coats are as a general rule 
preferable to one thick coat. 

The consistency and working properties of each paint should be carefully 
noted, and also a comparison made as to their opacity (body) and covering 
power. 

If an accurate comparison of the body and covering power is required, then 
the amount of paint necessary to cover a given area should be carefully weighed 
(see Covering Power of Pigments, Chapter XIV.). 

Two prepared boards should be painted with each of the paints under test, 
so that one can be hung outside and tested as to its durability and wearing 
properties under weathering influences, while the other is kept indoors. 

The time the paint takes to dry inside and out is carefully noted, since as a 
general rule those paints which require a longer time to dry are more durable and 
wear better on outside exposure than the quick-drying paints. On the other hand 
the fact should not be lost sight of that if the paint dry too slowly its surface is 
liable to pick up dust and tend to absorb moisture ; further, should by any chance 
rain fall before the surface has set hard then the paint will be apt to become soapy 
and streaky, and dry off patchy, or even wash off altogether in places. Under 
these conditions the durability and protective properties of the paint will be 
seriously interfered with, and after a few months’ exposure the paint surface will 
probably chalk badly and eventually wash completely off. 

The time a paint takes to dry outside depends on the nature and composition 
of the paint as well as on the temperature of the atmosphere and the general 
weather conditions prevailing at the time of painting. Cold, damp, foggy weather 
will naturally tend seriously to retard the drying operation, whereas warm, dry 
weather will accelerate it. 

A paint which takes longer to dry than eighteen hours on outside painting 
should be speeded up by the addition of paste or liquid driers (see Chapter XX.). 

The condition of the dry painted surface after it has set hard should be 
carefully examined and note taken as to its lustre (“face”) smoothness and 
freedom from coarse particles, its flowing properties and absence of streakiness 
or brush marks. 

The toughness and elasticity of the dry paint film may be tested by scraping 
it with a sharp knife. If it should show any signs of brittleness, then it may 
be taken for granted that the paint will wear badly and is only suitable for 
indoor use. 

The painted boards which are exposed outside for weathering tests should be 


26 THE CHEMISTRY OF PAINTS 


examined every month and note taken of any signs of deterioration or wear such 
as blistering, chalking, cracking or shelling off. 

A high-class paint should wear well for four or five years, when exposed to 
weathering influences, without showing any indications of cracking or shelling off. 
The best class of paints are those that wear down evenly, showing only a moderate 
chalking effect and leaving a surface which only requires washing down to render 
it suitable for repainting. 

Paints manufactured for particular purposes should obviously be tested 
out as nearly as possible under the conditions they are to be used in order to 
ascertain how closely they possess the properties required of them; for example, 
anti-corrosive paints should be tested out on iron work; priming paints, on both 
wood and iron, and so on. 


ming res hoe a 


The Inorganic and Organic Pigments. Their 
Preparation and Properties 


CHAPTER VI 


THE WHITE PIGMENTS 


THE group comprising White Pigments is not a very large one, but it includes 
amongst its members some of the most important and widely-used pigments at the 
disposal of the manufacturer of paints and protective coatings. Many of these white 
pigments, for example white lead and zinc oxide, are more or less familiar to every- 
one, and are in daily use, although their method of preparation and their properties 
may not be quite so well known. 

For the sake of convenience the white pigment group may be divided into 
two sections, viz. :— 

(a) The naturally occurring white pigments, and 

(6) The manufactured white pigments, i.e. those pigments which are produced 

by chemical means. 


(4) THE NATURALLY OCCURRING WHITE PIGMENTS 


In this group are those white pigments which occur in nature in a more or 
less pure state, and require only a simple process such as grinding and levigation 
to render them suitable for use. The following well-known and widely distributed 
natural occurring pigments are comprised within it, viz., barytes, whiting, terra 
alba, China clay, French chalk, white earth. 

These pigments are often classified under the name of “the inert pigments ” 
or “ extenders,” as their body and covering power is exceedingly small. 


Barytes (BaSO,) 
(Barium Sulphate, Schwerspat, Permanent White, Sulfate de Baryte.) 
Barytes was discovered by Scheele in 1774 in a mineral called terra ponderosa, 
or ponderous spar. Bergman gave it the name of barytes, from the Greek word 
“ barys ” (heavy). 
27 


28 THE CHEMISTRY OF PAINTS 


It occurs very widely distributed, as the mineral heavy spar, in various parts 
of England, Germany, America, Spain, Italy and other countries. Frequently it 
occurs associated with lead ores such as galena; and in the Derbyshire lead mines 
the workmen call it “ cauk.” 

The purity of barytes varies considerably according to the locality in which 
it is found ; moreover often in the same mine seams of barytes are obtained some 
of which are of a pure white colour whereas others are of a yellowish or greyish-red 
hue, due to the presence of iron. 

Sometimes large masses of crystalline barytes, in the form of large rhombic 
prisms, are met with, but the amorphous or non-crystalline variety is more usual. 

Manufacture——The manufacture or preparation of barytes for use as a pig- 
ment or base is very simple. The large masses of crude mined material are sorted 
out so that the whiter portions are separated from the reddish-yellow and discoloured 
portions, the latter being made use of in the preparation of the commoner grades 
of finished barytes. The crude material, after this preliminary grading, is then 
ground in large flat stone mills under water till the material is perfectly fine. 

This grinding process is a very tedious operation, and sometimes—especially 
in the more crystalline varieties—it is necessary to put the material through the 
stone mills from four to ten times before it is fine enough for use. 

The stones used in the mills must be exceedingly hard, and it has been found 
by experience that French stones give the best results, on account of their great 
hardness. 

As a rule the mills are arranged in series so that the ground material passes 
from one mill to the other till the requisite degree of fineness is attained. The 
ground material, as it comes from the mills, is conveyed into settling tanks, as in 
the usual process of levigation (see Chapter VII.), so that any coarse particles are 
separated out and ground over again. 

The material thus obtained is known as “ water-floated ” barytes, and requires 
to be bleached to make it suitable for the best grades of white barytes. 

This bleaching operation is carried out by the addition of a small percentage 
of sulphuric acid or hydrochloric acid, continual stirring being necessary so as 
to get complete admixture. Steam may be passed through to accelerate the 
operation. 

By means of this acid treatment all the iron which is present in the barytes 
is removed and a perfectly white product is produced. 

The barytes is next well washed till all the acid is removed, then dried and 
sieved, when it is ready for use. 

In many cases the sorted-out barytes is simply ground in the dry state three 
or four times through special stone mills till the required degree of fineness is 
secured. This is usually done in those cases where the barytes mined is of a 
somewhat soft amorphous character and readily lends itself to this operation. 

The ground barytes thus obtained is then subjected to a sifting process by 
means of compressed air; in this way “ air-floated”” barytes of an excellent degree 
of fineness is obtained. 


WHITE PIGMENTS 29 


It is usual to add a small trace of ultramarine blue during the grinding opera- 
tion, whereby the whiteness of the barytes is much improved. 

The barytes comes on to the market packed in 1 or 2 cwt. bags, or about 
8 cwt. casks, and is comparatively cheap. Owing to its cheapness it forms an ideal 
“extender” or adulterant for use in conjunction with other pigments, especially 
white lead on account of its high gravity and low oil consumption. 

Barytes is sold under twelve or more different grades, each varying as regards 
colour and fineness of grinding. 

These grades may be roughly divided into three, viz., Best Superfine White 
Barytes, Seconds Barytes, and Common Barytes. 

By far and away the best barytes that comes on to the English market is 
imported from Germany—this not only on account of its pure white colour, but also 
because of the excellence of its texture and the fineness of its grinding. 

This is due to the fact that in Germany there are very large deposits of naturally 
occurring soft amorphous heavy spars, and also, to a lesser extent, because owing 
to the cheap water power the cost of a large number of grindings which would 
be prohibitive in other countries does not add very materially to the cost of 
production. 

Spanish Barytes is of rather an open texture, and there is often associated with 
it a certain proportion of sulphate or carbonate of lime. 

English Barytes is unfortunately rather coarse in texture and inferior in colour 
as compared with that of the German. 

Properties and Uses.—Barytes or barium sulphate (BaSO,) is used in enormous 
quantities in the paint trade as an adulterant or “‘ extender” for mixing with other 
pigments whereby their cost is considerably reduced. Its value is dependent on 
the whiteness of its colour and the fineness of its texture or grinding. 

It is a heavy white pigment, and owing to its crystalline nature has always a 
slight gritty feel. It is one of the heaviest white pigments or “ extenders’ known, 
and has a specific gravity of 4-48. Its oil absorption is very low, and it only requires 
about 8-5 per cent. of oil to grind it into a paste form. 

Barytes is practically insoluble in water (100 gms. of water at 10° C. dissolve 
0002 gms. BaSO,) and is quite permanent; it is not attacked by either acids or 
alkalies, and can be ignited without undergoing any change. 

As previously stated it is largely employed, because of its low oil absorption, 
as an adulterant for white lead. 

Barytes has practically no covering power or body; hence owing to its lack 
of strength and transparency it makes an excellent base for aniline colours, these 
colours not being in any wise affected by it. 

The use of barytes in paints cannot be regarded simply in the light of an 
adulterant, since by its use in, for example, Brunswick greens, the tones of the 
associated pigments (chrome and blue) are thereby much enhanced, and at the 
same time a paint is produced of much superior working properties and at 
considerably less cost. 

Analysis of Barytes—A complete analysis of a barytes is as a rule not required, 


30 THE CHEMISTRY OF PAINTS 


as the qualitative tests are quite sufficient to indicate whether the material is up 
to the required standard. 

The chief requirements of a first-class barytes are that it shall be of a good 
white colour and fine texture. 

Colour and Fineness;—The simplest way to test the colour and fineness is to place 
a portion of the sample on a white palette alongside of the standard and add a few 
drops of turpentine to each, and note the resultant 
colour. A creamy white is always to be preferred 
to a greyish white. 

The texture is next examined by grinding the 
sample moistened with turpentine on the porcelain slab 
with an iron palette knife. The comparative degree of 
fineness and texture can at once be recognised after a 
very little experience. 

Samples of barytes containing sulphate or carbonate 

of lime may be recognised by their somewhat open 
texture; if silica be present then the barytes feels 
harsh, and rapidly discolours after a little grinding, 
owing to the wearing action of the hard silica on the 
iron palette knife. 
' A quantitative estimation of the amount of coarse 
) particles in a barytes may be made by putting a 
weighed quantity through a series of sieves of different 
degrees of fineness and weighing the residue. 

A still more reliable method consists in using an 
Elutriator (see Fig. 8). The Elutriator proper consists 
. of ashort tube of similar diameter to an ordinary burette, 
z.e. such that 1 c.c. of fluid occupies 1 cm. of length. 
It is open at the top and reduced at the bottom to about 

Fic 8 ul Geatieaone, 2 mm. bore. This end is curved up in a U form. 

Into the upper end fits a perforated rubber cork bearing 
an inverted U tube. The lower end is connected by means of rubber tube to 
the lower of two tandem stopcocks A and B. A removable pinchcock fits 
this rubber tube. The upper stopcock is connected to a water-pressure 
regulator which, by means of simply raising or lowering with the aid of a 
cord and pulley, regulates the speed of flow through the Elutriator. 

Upon erection, the cock A is fully opened, the regulator raised to the point 50, 
and the cock B is adjusted till just 50 c.c. of water are discharged from the inverted 
U per minute. The cock B is never touched afterwards, and any point on the scale 
corresponds to a flow of that number of c.c. of water per minute through the 
instrument. 

In use the Elutriator is detached, half filled with water, a weighed quantity 
of the barytes dropped in, the open end corked, and the contents thoroughly shaken. 
It is then placed in position and the flow of water established for five minutes. It is 








WHITE PIGMENTS 31 


removed, half emptied by decantation, corked, shaken, and the flow continued for 
another five minutes. 

Similarly a third shaking and washing is given, the contents being finally 
passed through a weighed filter, dried in the steam oven and weighed, giving the 
percentage of coarse matter. The rate of flow must be found experimentally to 
suit each user’s requirements and also varied according to the heaviness of the 
barytes under test. 

Free Acid.—As acid is used in the bleaching of barytes it is necessary to make 
sure that it has all been washed out, and that the barytes is perfectly neutral. 

The easiest method of doing this is to place a small portion of the sample in 
a watch glass, adding a few drops of distilled water, and then introducing a strip 
of blue litmus paper. Any reddening of the latter will indicate the presence of 
an acid. 

Iron Carbonates, Lime, etc.—Boil a portion of the sample, say 1 gm., with a little 
hydrochloric acid. Any effervescence indicates carbonate of lime or barium. 
Filter off, wash well, dry and weigh. This gives the percentage of barium sulphate 
provided no silica is present. 

To the filtrate add (1) barium chloride solution. A white precipitate indicates 
calcium sulphate. 

(2) Three drops of nitric acid and a little potassium ferrocyanide solution. A 
blue coloration indicates iron. 

If carbonates be present then test for calcium and barium in the filtrate in the 
usual way. 


Wuitine (CaCQO,) 


(Paris White, Spanish White, Chalk, Calcium Carbonate, 
English White, Kreide, Craie.) 


The vast masses of limestone,- chalk and marble which are found in every part 
of the world are combinations of lime and carbon dioxide, and are represented by 
the formula CaCO, (calcium carbonate). 

Chalk is essentially a rock of organic origin, and the microscope shows that it 
consists largely of the shells of minute organisms. Calcium carbonate is dimorphous, 
and occurs in nature in two well-defined crystalline forms, viz., in the form of rhombic 
crystals as aragonite, and in trigonal crystals as calespar or Iceland spar. Marble 
is made up of minute crystals of calcite or calespar. 

Iceland spar is a calcium carbonate of a very high degree of purity, and can be 
obtained in clear crystalline blocks containing 99-9 to 100 per cent. CaCOs. 

Chalk and limestone are found very abundantly on the English coasts, and in 
various other parts of the country, in a more or less pure condition, though often it 
is associated with magnesium carbonate, clay and silica. 

Marl is a mixture of limestone and clay. 

Manufacture—The crude quarried chalk is prepared for use as a pigment by 
grinding under water and levigating to separate the coarser material. The wet 


32 THE CHEMISTRY OF PAINTS 


whiting from the settling tanks is dried on a long hearth heated by fires, care being 
taken not to overheat, otherwise lime may be produced. 

The dried whiting is then sieved and bagged ready for use. Whiting is sold 
in several varieties. The purest and finest is known as Paris white, the second 
under the name of Gilders whiting is often sold in large lumps or “nubs.” The 
commonest variety of all is of course called simply whiting. 

The crudest material from the early settling tanks is put on the market under 
the name of whiting sand; it is of a coarse texture due 
to the large amount of silica associated with it. 

Properties and Uses.—Paris white or whiting is of a 
pure white colour and has a soft texture. Its specific 
gravity is 2-5. It is a bulky pigment, and requires a 
comparatively large amount of oil to grind into a paste 
(18 per cent.). 

It is quite stable to light and is unaffected by 
sulphuretted hydrogen. It may be mixed with all 
pigments without change. 

It is practically insoluble in water (100 gms. dissolve 
00018 gms.), but is more soluble in water containing 
carbon dioxide, forming acid carbonate of lime CaCOg, 
H,CO;. The temporary hardness of water is due to this 
acid carbonate of lime being dissolved in it and may be 
removed by boiling. 

It is soluble in all dilute acids with effervescence due 
to the evolution of carbon dioxide, thus :— 


On strong ignition the carbonate of lime is decomposed 
with evolution of carbon dioxide and formation of 


Fig. 9.—Scurirrer CO, quicklime —— 
APPARATUS. Cad O,2Ca O i CG Op». 


Paris white or whitening has no body or covering power when ground in oil, 
but has a transparent dirty yellowish appearance. On the other hand, it has 
splendid covering power in water, and for this reason is used in very large quantities 
in the manufacture of distempers and kalsomines. It is also largely used when 
ground into a stiff paste with linseed oil as putty for glaziers’ use. 

Analysis——An analysis of whiting is rarely called for, as its value is judged by 
its colour, and the fineness of its texture and freedom from grit. 

If required all that is necessary is to dissolve in hot dilute hydrochloric acid 
and filter off and weigh the insoluble matter, equals silica (Si0,). 

The calcium may be estimated by adding ammonia and precipitating with 
ammonium oxalate (after the removal of any iron or alumina that may be present) 
and igniting and weighing as lime (CaQ). 

The carbon dioxide may be estimated in the Schrétter apparatus (see Fig. 9). 





WHITE PIGMENTS 33 


Lime (CaQ) 
(Quicklime, Calcium Oxide.) 


Quicklime or lime is made on the large scale in Buxton and elsewhere by 
heating limestone in lalns along with coal. The burning of the coal in the presence 
of the air which is drawn through the kilns produces a white hot heat whereby the 
calcium carbonate is decomposed, carbon dioxide being evolved and lime left 
behind. 

CaCO,—=Ca0+CO, or CaCO,+C=Ca0+2C0. 


When water is added to lime combination takes place and a considerable amount 
of heat .is evolved, calcium hydroxide being formed. The lumps of quicklime 
fall to powder when thus treated, slaked lime being produced; with sufficient water 
to bring it to a creamy consistency “ milk of lime ” is produced. 


CaO +H,O=Ca(OH),. 


Lime is used, mixed in water, for lime washing. It is also used for making 
mortars and cements; and in the varnish industry as a hardener for rosin 
(see Chapter XVIII.). It is likewise employed for many purposes which it is 
unnecessary to mention here. 


TERRA ALBA 
(Gypsum, Calcium Sulphate, Light Spar, Gips.) 


Gypsum occurs native in large quantities in various parts of the world. It 
is mined extensively in this country in Derbyshire, Staffordshire, and other localities. 

It occurs as the anhydrous sulphate CaSO, as anhydrite ; and in the hydrated 
form CaSO,, 2H,O as gypsum, alabaster, selenite, agalite, etc. 

The natural deposits of gypsum or lightspar are prepared for use in the pigment 
industry by a simple process of grinding much in the same way as described under 
barytes. 

Properties and Uses.—Terra alba possesses a good white colour; it has a poor 
body and is rather transparent, hence has no real covering power. Its specific 
gravity is 2-3. Its texture is very open or woolly ; hence it is not used very much 
with other pigments except in the case of ultramarine and lead chromes. With 
lead chromes it replaces whiting as the latter has a tendency to redden the shade 
of yellow chrome. 

Venetian reds contain large quantities of terra alba, but this has been produced 
by, as a rule, the action of calcium carbonate on the ferrous sulphate during the 
ignition process in the manufacture of this class of red pigments. 

Gypsum contains 2 molecules of water of crystallisation and so has the formula 
CaSO,.2H,0. 

Plaster of Paris—When gypsum is heated to about 140° C. it is rendered 
anhydrous, and is converted into plaster of Paris; and when this is made into a 
paste with water it rapidly hardens, and is used as a cement. 


34 THE CHEMISTRY OF PAINTS 


Calcium Sulphate possesses the peculiar property (lime resembles it in this 
respect) of being somewhat less soluble in hot water than cold, requiring over 
500 times its weight of water at 100° C., but only 400 times at 35° C. to 
dissolve it. Calcium sulphate will dissolve when boiled for a long time with excess 
of hydrochloric acid. 

It is largely used by paper stainers, and for “‘ weighting” cotton goods; also 
in distempers. 


Cuina CLAY 
(Kaolin, Pipe Clay.) 


China clay or kaolin is widely distributed in England, France, Germany, and . 
other places. Some of the finest China clay for use in the manufacture of pottery is 
obtained from Cornwall. 

When potash felspar (K,0, Al,O3, 6810.) and many other natural alumino- 
silicates are exposed to weathering influences they are in process of time converted 
into an insoluble white crystalline or amorphous (colloidal) powder, such as China 
clay. Hence the deposits of China clay may be said to be due to the weathering 
of the alumino-silicates. 

Granitic rocks with felspar as a matrix disintegrate in process of time, leaving 
the clay behind mixed with the more resistant varieties of mica, quartz, and other 
minerals, which originally formed the granitic rock. 

Manufacture.—China clay is obtained in a more or less pure state, that is free 
from the unweathered quartz, mica, etc., by a simple process of washing and settling 
or levigation. The settling tanks are so arranged that all the lighter mica, which 
comes over after the heavier quartz has settled out, is caught in a series of large 
troughs, thus allowing the material that finally passes over into the last settling 
tanks to be practically pure China clay; this is dug out of thesettling pits and 
dried. 

Properties and Uses.—China clay is essentially an hydrated silicate of alumina, 
which has very nearly the empirical composition—Al,0,.2810,.2H,0. 

It is a white powder with an extremely soft and fine texture. Its specific 
oravity is about 2-2. It is a very bulky material, hence requires a lot of linseed oil 
to grind it into a paste form. Being transparent in oil, it lacks body and covering 
power. It is used extensively in paints as a suspender for preventing settling and 
is very useful in dipping paints (see Chapter III.), for on account of its low specific 
gravity it keeps the pigments associated with it in suspension. In addition, China 
clay is largely used as an inert base on which to strike or precipitate aniline dye- 
stufis. It is quite permanent and stable to light, and is not affected readily either 
by acids or alkalies. 

In the manufacture of ultramarine blue it plays an important part 
(Chapter VIIT.). 


WHITE PIGMENTS 35 


MaGnesium SILICATE 
(Talc, Steatite, French Chalk.) 


Magnesium silicate occurs in nature as olivine Mg,Si0,; serpentine Mg,Si,0, 
+2H,0; talc, soapstone or steatite 3MgO0.48i0,H,O. Asbestine, asbestine pulp, 
asbestos, and meerschaum are double silicates of calctum and magnesium. 

Tale or French chalk has a soft unctuous feel, and on account of its low specific 
gravity is much used in paints to prevent settling. It is very inert and has properties 
similar to those of China clay. It is easily recognised under the microscope by the 
fibrous structure of its particles. 

Silica (Silew).—Silica ($102) is one of the most important compounds forming 
the crust of the earth. In a crystalline condition it occurs as quartz or rock crystal 
and tridymite. In an amorphous form it is met with in ernormous quantities in 
the deposits known as kieselguhr. This substance consists of the remains of extinct 
diatomaccze and is come across in various parts of Germany and America. 

Diatomaceous earth, also called tripoli, kieseleuhr, Fuller’s earth, or infusorial 
earth, is largely used as a bleaching agent for oils; in the manufacture of dynamite, 
cement, and for many other purposes. 

Silica obtained by crushing quartz very finely and sieving through 120-200 
mesh sieves comes on to the market as a harsh-feeling, coarse-grained white powder. 
In the paint trade it is largely employed, ground in oil and varnish, as a wood filler 
or priming paint for wood for filling up the grain before staining and varnishing. 


STRONTIUM SULPHATE 
(Strontium White.) 


This material occurs naturally as the mineral celestine (SrSO,). It is sometimes 
used as a substitute for barytes, but is not so satisfactory, as owing to its higher 
specific gravity it absorbs more oil. 

Its properties are very similar to those of barytes, from which it may, however, 
be readily distinguished by the bright crimson colour which it gives in the Bunsen 
flame as compared with the well-known green barium flame which is characteristic 
of barytes. 

Barium Carbonate (BaCO,).—This substance is found in Germany, England, and 
America native as witherite. It is practically never used as a pigment in this 
country, though a certain quantity is used in America as an extender for readily 
mixed paints. 

White Earth—This material is similar in composition to the native augites 
described under Green Earth (see Chapter IX.), and is a magnesium aluminium silicate. 
It is of a transparent white colour, and like green earth has the property of fixing 
basic dye-stufis. In fact, with dye-stufis such as methyl violet and methylene blue, 
where it is essential that the clearness of the tones should be retained, it is used in 
preference to green earth. 


36 THE CHEMISTRY OF PAINTS 


(B) THE WHITE INORGANIC CHEMICAL COLOURS 


Under the classification of White Inorganic Chemical Colours are white pigments 
which are produced by chemical means, as distinguished from those naturally 
occurring white pigments which have already been described. 


BLANC-FIXE 
(Permanent White, Precipitated Barium Sulphate.) 


Blanc-fixe, or, as it is sometimes called, artificial barytes, has the same com- 
position as the naturally occurring barytes or heavy spar, BaSO,; in fact, it is 
precipitated barytes. It is produced as a fine white precipitate whenever a solution 
of a sulphate or sulphuric acid is added to a barium salt, thus :— 

BaCl,+H,SO,—BaSO,+2HCI or Ba(NO;),-+-Na,SO,—BaSO, +2NaNO,. 

It is marketed either as a fine white powder or as a paste or pulp containing 
about 20 per cent. water. 

Manufacture—The raw materials that are used in the manufacturing scale 
for the production of blanc-fixe are either natural barytes or witherite (BaCO,). 
The cheapest and at the same time the most convenient process (and which is in 
general use), is to take the mineral witherite as the starting point. 

The witherite is ground to a fine powder and decomposed in tanks by means of 
hot dilute hydrochloric acid, whereby great effervescence takes place owing to the 
liberation of carbon dioxide. The barium chloride solution thus formed is allowed 
to settle, and is then run through filters into precipitating vats. Sulphuric acid 
is added till all the barium present is thrown down as barium sulphate. Glaubers 
salts (sulphate of soda) or other cheap sulphates may be used in place of sulphuric 
acid to precipitate the barium sulphate. 

The precipitate of the blanc-fixe thus formed is well washed till quite neutral 
and free from all soluble matter. It is then filter pressed, and sold in the form of 
a paste containing about 20 per cent. of water; or if required in powder form it is 
dried in vacuum stoves. 

The course of the reactions that take place during this operation may be 
expressed by the following equations :— 

BaCO,;+2HCl=BaCl,+H,0+C0,. 
BaCl, +H,SO,=BaSO,+2HCL. 


The ground witherite can also be treated directly with hot dilute sulphuric 
acid, though in this case the blanc-fixe thus produced requires careful sieving to 
remove all the impurities that may be present in the raw material. 

The reaction proceeds as follows :— 


BaCO3,;+H,SO,=—BaSO,+H,0-+CO,. 
As the decomposition of the witherite by treatment with the hot dilute acids 


is always accompanied by great effervescence due to the liberation of large quantities 
of carbon dioxide, so care must be taken to provide plenty of ventilation. 


WHITE PIGMENTS 37 


The manufacture of blanc-fixe from natural barytes or heavy spar is carried 
out as follows :— 

The finely ground natural barytes is calcined with coal or charcoal in a rever- 
beratory furnace at a red heat, barium sulphide being thereby produced as under :— 


BaSO,+4C=BaS+4CO. 


The barium sulphide is then digested with hot dilute hydrochloric acid, sulphuretted 
hydrogen is evolved and barium chloride remains in solution :— 


BaS +2HCl=BaCl,+H,S. 


The solution thus produced is allowed to settle, then filtered to remove all solid 
impurities. Sulphuric acid, or sulphate of soda or magnesium solutions, are next 
run in causing barium sulphate to be precipitated. This is washed and dried as 


before. 
Ba€l, +Na,SO,=BaSO,+2NaCl. 


Considerable quantities of blanc fixe are also obtained as a by-product in the 
manufacture of hydrogen peroxide from barium peroxide, thus :— 


BaO,-+H,S0,—BaS0,+H,0,. 


Properties and Uses.—Blanc fixe is a white powder possessing an extremely 
fine and soft texture. It is quite permanent, and as it is simply a precipitated barium 
sulphate its general properties—with the exception of its fine texture—are similar 
to those of barytes and need not be further described. It is largely used as an inert 
base for coal tar dye-stufis (see Lakes, Chapter XIII.), and also as a filler or extender 
for enamel paints where a fine extender material is essential. 

Its specific gravity is 4-3. On account of its bulkiness it requires more oil than 
barytes to convert into paste form ; and by reason of its lightness and non-settling 
properties it is largely used in dipping and spraying paints. Owing to its amorphous 
character it has more covering power than barytes ; its cost, however, is about twice 
as great. 

Satin White——This product is a mixture of alumina and calcium sulphate. It is 
prepared by mixing the equivalent proportions of freshly slaked lime—mixed with 
water to form a cream—and sulphate of alumina or alum solutions. The reaction 
may be expressed by the following equation :— 


3Ca(OH),+Al,(SO,);=3CaS0,+Al,(OH),. 


The precipitate of satin white thus formed is well washed and may be filtered 
and dried, but is more usually sold in the pulp form. Satin white is a white pigment 
with moderate covering power. Its chief use is in the paper trades. 


Atumina (Al,0;) and Atumintum Hyproxipe (Al,(OH).) _ 
(Tonerdehydrat.) 


Alumina occurs in nature in the crystalline form as emery and corundum. 
Aluminium hydroxide is precipitated from solutions of alum or sulphate of alumina 
by caustic alkalies (soluble in excess); ammonia or ammonium carbonate. 


38 THE CHEMISTRY OF PAINTS 


It is also precipitated from alkaline aluminates by carbon dioxide, which is | 
the method in use for the manufacture of the material on the large scale. The 
reaction may be expressed thus :— 

3Na,.0.Al,03;+3C0,—A1,03+3Na,COsz. 
The hydroxide which is prepared by the addition of ammonia or ammonium 
carbonate, or caustic alkalies, is a bulky, flocculent, gelatinous precipitate possessing 
the property of acting as a mordant in carrying down dye-stuffs in solution and 
absorbing them. On this account it is largely used in the manufacture of Lakes 
(see Chapter XIII.). The production of the hydroxide of alumina may be 
represented by the following equation :— 


Al,($O,)3-+6NH,OH=Al,(OH),+-3(NH,),80,. 


The freshly precipitated alumina hydroxide (often called alumina) is readily soluble 
in excess of caustic alkalies such as caustic soda, and in dilute acids. 

By igniting the hydroxide the whole of the water is driven off and the anhydrous 
oxide Al,O, is obtained as a pulverent white powder. 

Aluminium hydroxide is largely used as a base by the lake manufacturer owing 
to its mordant properties. It is rather transparent, hence the lakes formed with it 
are deficient in body but possess bright clean tones and strong staining properties. 
The lake manufacturer produces his “ alumina” base in the following way: Alum, 
or 18 per cent. sulphate of alumina (iron free quality), is dissolved in about twenty 
times its weight of hot water. Then a dilute solution of soda crystals, soda ash, or 
ammonium carbonate is run in, with continual stirring, till all the alumina is pre- 
cipitated. The precipitate is well washed by decantation with cold water till 
perfectly neutral and free from all soluble matter. 

It is then ready to be used as a base for fixing on the various dyestufis—either 
natural or artificial—which it is desired to precipitate. 

The following example will give a clear idea of how this process is carried 
out. 

Process 1. Alumina Hydrate Base.—200 lbs. of sulphate of alumina are 
dissolved in 500 gallons of hot water (110° F.). Stir in slowly 90 lbs. of soda ash 
(or its equivalent of soda crystals or ammonium carbonate) dissolved in 90 gallons 
of cold water. Wash well till free. 

The above proportions should give about 50 lbs. of dry alumina hydrate. 

The precipitate is used in the pulp form. If it should be required in the 
dry state, care must be taken to dry at a very low temperature otherwise a 
tough, horny mass of alumina will be produced, which will be quite unsuitable 
as a base. 

As mentioned above the base thus produced is of a very transparent nature, 
and on account of this the lake manufacturer very often makes an addition of blanc- 
fixé (precipitated barytes) so as to give more body to it. This is especially the 
case where the lake is going to be used as a body colour. 

The following process for the manufacture of an alumina blanc-fixé base will 
illustrate the methods in vogue for the preparation of this base. 


WHITE PIGMENTS 39 


Process 2. Alumina Blanc-fixe Base. 
Mix 200 lbs. sulphate of alumina, and 
90 ,, soda ash (as in process 1). Stir into this 
210 ,, barium chloride dissolved in 100 gals. water. 
Wash till free. This gives about 250 lbs. of dry alumina blanc-fixé base. 


Waitt LEAD 


(Flake White, Kremnitz White, Bleiweiss, Ceruse, Blanc de Plomb, 
Blanc d’ Argent.) 


White lead is a basic lead carbonate represented by the formula 2PbCO,,.Pb(OH),. 
It was known to the ancients; Theophrastus, Pliny, and Vitravius describe its 
method of preparation from metallic lead and vinegar. 

At the present time white lead is probably the most important white 
pigment that is manufactured by chemical means, and the yearly output of this 
material is enormous. 

There are a large number of factories in England, Germany, and America 
engaged in the manufacture of this pigment, and the processes in operation ior the 
conversion of blue lead into white lead are very varied. 

Owing to its poisonous nature special regulations and legislation have been 
introduced from time to time to minimise the risks attendant on the manufacture 
and use of this pigment. In fact, in some countries, e.g. France, its use has been 
prohibited and its place taken by zinc oxide; in this country it has been proposed 
that its use should be abandoned. 

The question of the use of white lead was investigated by two Committees 
appointed by the Home Secretary in 1911. Their reports, issued in 1915 and 1920, 
were unfavourable to its continued use; and in the belief that adequate substitutes 
were available, they recommended that the use of white lead for paint material 
should be prohibited. No effect was, however, given to this recommendation. 

Overwhelming evidence of the failure of many of these substitutes led to the 
appointment by the Home Secretary in 1921 of a new Committee, with Sir Henry 
Norman as Chairman. This Committee was unable to support the recommendations 
of its predecessors, and was of opinion that for outside painting and for certain 
kinds of internal painting “ there is at present no efficient substitute for white lead.” 

This is also the view of Professor H. E. Armstrong and C. A. Klein, who have 
studied the subject exhaustively. 

The League of Nations at Geneva has also carefully considered the whole of the 
facts brought before its notice in regard to the injurious and poisonous nature of 
this pigment. The subject is a highly controversial one and outside the scope of 
this book. 

Many substitutes for white lead have been offered at different times under such 
names as non-poisonous white lead, such as sulphate of lead, and others ; but these 
have all been found to be lacking in those essential properties of density and body 
which are characteristic of all well-made white leads. 


D 


40 THE CHEMISTRY OF PAINTS 


Other non-poisonous white pigments, notably zinc oxide, lithopone, antimony 
white, and recently titanium white, have been proposed as alternatives to white 
lead; and, at the present time, enormous quantities of zinc oxide and lithopone 
are consumed yearly in the manufacture of white paints, for both inside and outside 
work. 

It cannot be denied that as regards density, body and obscuring power, white 
lead is pre-eminent (though sometimes it is claimed that titanium white is its 
equal; its price, however, is twice as high. See Titanium White, page 56). 
Moreover, as a priming coat for protective work on outside structures it is unsur- 
passed; in fact, the durability and hard-wearing properties of white lead are 
altogether remarkable. 

Perhaps it is only fair to add that manufacturers of white lead assert that as 
a result of the stringent regulations that are now in force as regards ventilation, dust, 
and cleanliness, cases of lead poisoning are practically non-existent in the works 
engaged in the production of this pigment. Further, that if users were equally 
careful to carry out faithfully the rules laid down for them, lead poisoning would be 
a negligible risk. 

The manufacture of white lead on the large scale is very old; and for various 
reasons it is supposed that the first works to be erected for its production on a 
commercial scale were situated in Holland. The “ Dutch process,” as it is called, 
has been carried on for many hundreds of years in Holland; and even up to the 
present time the old Dutch or stack process is in use in this and other countries 
and the white lead thus produced is still the most highly esteemed on account of its 
unsurpassed density and body. 

The Manufacture of White Lead.—White lead or basic carbonate of lead 
(2PbCO;Pb(OH),) is manufactured by a great many processes. Innumerable 
patents have been taken out at different times for the production of this pigment, 
and it would be quite impossible within the space at our disposal to describe, or 
even mention, a tenth of them. The reader who is particularly interested in the 
subject is referred to the special treatises and patent specifications dealing with 
it (see Bibliography). 

We will now describe the Dutch process, or Stack process, as it is more 
commonly called, for the manufacture of white lead. 

1. The Dutch Process (“‘ Stack” White Lead Process).—This process, as stated 
above, has been carried on in Holland for many hundreds of years—it was said to 
have been “old” in 1662—with little change as regards the main essentials. 
From Holland it spread to other countries till it is now employed in all parts of 
the world. 

Shortly, it depends on the action of acetic acid upon metallic lead in the 
presence of moist air and carbon dioxide. 

The molten metallic lead, after the removal of the scum on the top, is cast 
into rough gratings, or else into thin strips which are rolled up spirally, care being 
taken to see that the strips of lead are thin and uniform, so that the maximum 
efficiency in corrosion will take place. 


WHITE PIGMENTS Al 


The metallic lead used by the white lead manufacturer should be as pure as 
possible, as even a small trace of such foreign metals as silver, copper, bismuth, 
cadmium, antimony, and iron would cause a discoloration of the finished product. 

The corroding pots used in the Dutch process are made of earthenware glazed 
inside, and are provided with shoulders on which the strips of lead or gratings are 
supported (see Fig. 10), so that they do not come in direct contact with the acid. 
A layer of 3 per cent. acetic acid (in the old Dutch process vinegar) is first placed 
in the pot. 

The pots vary in size, but as a rule average about 8 inches high by 4 inches 
in diameter. They are placed upon a thick bed of spent tan bark from the leather 
tanning yards (in the original process 
dung was used, but owing to the 
evolution of sulphuretted hydrogen, 
which discoloured the lead, it was 
replaced by various substitutes) upon 
the floor of a shed and covered with 
planks. 

Upon these planks another layer 
of tan bark is spread, and a second 
row of pots similarly charged. In 
this manner the layers of pots are 
built up to the roof of the shed. 
The whole is then allowed to remain 
for about twelve weeks. At the end 
of this time most of the lead will 
have been transformed into compact Fie. 10.—Waire Leap Corropine Por. 
masses of white lead. 

Such stacks are very large, say 15 feet square by 20 feet high, and contain 
many tons of lead; and about 70 gallons of dilute acetic acid to the ton of metal. 

The heat developed by the fermenting tan volatilises the acetic acid, which 
results in the formation of a basic lead acetate thus :— 


2Pb+2H(C,H;0,)-+-0,=Pb(C,H302)2,Pb(OH)p. 

The basic acetate so formed is decomposed by the carbon dioxide evolved 
during the fermentation of the tan bark with the production of a mixture of 
normal lead acetate, and basic lead carbonate thus :— 

3[Pb(C,H,0.)., Pb(OH),]+2C0,= 
3Pb(C.H3;0.).+2PbC03, Pb(OH).+2H,0. 
The lead acetate in the presence of air and moisture reacts upon a further portion 
of the lead, forming more of the basic acetate of lead, which is once more decom- 
posed by carbon dioxide :— 
2Pb(C,H,0,).+2Pb+0,+2H,0 = 
2[Pb(CyH;02). Pb(OH),. 






































A2 THE CHEMISTRY OF PAINTS 


In this cycle of reactions, therefore, the acetic acid acts as a carrier, a com- 
paratively small quantity being able to convert theoretically an indefinite amount 
of lead into white lead. 

At the end of the period allowed for the complete conversion of the metallic 
lead into white lead the stacks are unloaded, great care being taken to ensure that 
none of the spent tan falls into the pots. 

On opening the pots it will be found, if the operation has been carried out 
properly, that practically all the acetic acid has disappeared and that the strips 
of lead are nearly all corroded away, leaving a thick deposit of white lead. The 
pots are emptied out, and the contents thoroughly ground through rollers and 
sieved so as to remove all the metallic lead that may be present. The separated 
blue lead is remelted to be used over again. The white lead is thoroughly washed 
to remove all the lead acetate, ground, filter pressed, dried and sifted. The first 
wash liquors containing the sugar of lead are treated so as to recover this material. 

The main objections to the Dutch or Stack process are (1) the great length 
of time required for the conversion of the blue lead into white lead, and (2) the 
fact that the white lead thus produced, although unsurpassed for opacity, density, 
and body, is yet somewhat lacking as regards the purity and whiteness of its 
colour. For these reasons, among others, many attempts have been made to 
speed up the process, and at the same time produce a white lead of a better 
colour. The most important of these processes is what is known as the 
chamber process. 

The Chamber Process or the German Process.—The chamber process for the 
manufacture of white lead was first introduced in Germany about the year 1750. 
The earliest processes were simply a modified or improved form of the Dutch 
process, and were carried out as follows :— 

The strips of metallic lead were suspended in wooden boxes, on the floor of 
which were placed a mass of fermenting grape husks, and other vegetable material, 
whereby acetic acid and carbonic acid were generated. The boxes were put in a 
warm room, and the temperature kept at about 50° C. 

The heat generated in the Dutch process, as described above, was generated 
by the natural fermentation of the tan barks, whereas in the chamber process 
artificial heat is used by means of which the fermentation is accelerated at will, 
while the acetic acid vapours along with the moisture and carbon dioxide which 
are evolved, corrode the lead, converting it into white lead. 

Later improvements consisted in partly replacing the fermentation materials 
by vinegar, which was simply poured into the box. 

In the modern chamber process the vinegar, or weak acetic acid, and the 
carbonic acid are both prepared outside the chambers and passed in along with 
steam. Further, the lead is “feathered” or rolled into very thin long strips and 
hung up on wooden racks in a large brick chamber. 

These chambers when full hold from five to ten tons or more of metallic lead, 
and the racks holding the strips of lead are so arranged as not to interfere with 
the efficient circulation of the gases and steam. 


WHITE PIGMENTS 43 


When the chamber has been fully charged, all the doors and windows are 
closed, and the acetic acid is supplied to the chambers in the form of vapour by 
boiling weak acetic acid (generally wood vinegar) in copper pans. 

The acetic acid vapour and steam, accompanied by air, are passed through 
the chambers for two or three days whereby the basic acetate of lead is formed. 

On the completion of this stage, carbon dioxide, obtained by burning charcoal 
or coke, is introduced in a steady stream together with more acetic acid vapours 
whereby the acetate of lead is converted into white lead. At the end of about 
four weeks the process is finished. The chambers are emptied, and the white lead 
recovered in the same way as described under the Dutch process. 

The Chamber process for the manufacture of white lead is not quite so simple 
as would appear from the above description, and very great care must be taken 
at all stages of the process if a good coloured and dense opaque white lead is to 
be obtained. 

Too much carbon dioxide, if introduced at too early a stage, will tend to 
produce an extensive amount of carbonate of lead, which would cause loss of 
opacity and density. The amount of air, moisture or steam, and acetic acid 
introduced all require to be regulated to a nicety to secure the best results. Hence 
long experience and very careful supervision are necessary to the successful carrying 
out of this process. 

The white lead obtained by the chamber process is superior in colour to that 
of the Dutch process, but does not equal it as regards density and opacity. 

The chamber process, with various modifications, is now very extensively 
worked in this country, Germany, and the United States; and by far the greater 
part of the lead that comes on to the market at the present time is made by this 
method. 

The French or Clichy Process—Thenard in 1801 showed that when carbon 
dioxide is passed through a solution of basic lead acetate white lead is precipitated, 
whilst acetate of lead remains in solution. Moreover, if this lead acetate is boiled 
up with litharge a portion of this body is taken up whereby basic lead acetate is 
again reformed. A process based on this reaction was employed by M. Roard 
about 1835 in a large factory near Paris, and the product thus obtained was sold 
under the name of Clichy White Lead. 

The reaction that takes place in the French or Clichy process may be expressed 
thus :— 

1. Pb(C,H,0,).+2Pb0+2H,0=Pb(C,H,0,),, 2Pb(OH),. 
2. 3[Pb(C,H;0,),, 2Pb(OH),]+400,=2[2PbC0,; Pb(OH),]+3Pb(C,H,0.).+4H,0. 

The plant used in this process is comparatively simple, the method of working 
being carried out as follows :— 

A solution of basic lead acetate is made in this manner, viz.: A solution of 
neutral acetate of lead (sugar of lead) is boiled in a large wooden vat, provided 
with a steam pipe, with litharge till it is all taken up and the basic acetate of lead 
formed. 

It is, however, more usual to make the sugar of lead in the white lead works 


4A, THE CHEMISTRY OF PAINTS 


itself by the action of acetic acid upon metallic granulated lead, or still more 
quickly by dissolving litharge in dilute acetic acid. 

The hot solution of basic sugar of lead of the required density is clarified 
before use to remove any extraneous impurities, and then run into a large wooden 
precipitating vat into which dip a large number of pipes, all of which are connected 
to a large main pipe through which the carbon dioxide is passed. 

The carbon dioxide may be obtained by burning charcoal or coke, or liquid 
carbon dioxide contained in large steel cylinders may be used. 

The carbon dioxide is passed into the basic sugar of lead under slight pressure till 
all the basic carbonate has been precipitated and the top liquor is slightly acid. 
This takes about sixteen hours. At the end of this period the white lead is allowed 
to settle out and the supernatant clear liquid is pumped off and returned to the 
first vat, where it is again boiled up with more litharge to convert it into the basic 
acetate to be used over again. In this way the process is a continuous one, the 
same amount of sugar of lead being used over and over again ; in practice, however, 
there is always a certain loss and the liquors require making up from time to time, 

The white lead precipitate thus obtained is well washed, filtered, pressed 
and dried. 

The product obtained by this process is of a very nice white colour, but is not 
equal in body or opacity to that of either the Stack or Chamber process. It is 
also liable to vary considerably, so that the product is not quite uniform. 

There are many modifications of the French process in operation for producing 
white lead from solutions of lead salts by the action of carbon dioxide, but as they 
are all based on the process detailed above it is unnecessary to describe them. 

Kremnitz White Lead Process.—This process was originally carried on at 
Kremnitz in Hungary, and the white lead produced by it is considered to be the 
whitest, and, at the same time, densest or most opaque that is made. It is usually 
imported from the Continent in 56 lb. boxes, the white lead being cut up into 
squares or cakes and packed separately in paper. 

It is of an extremely dazzling whiteness, and often smells strongly of acetic 
acid. It is mainly used by artists under the name of flake white or Kremnitz 
white. 

The process is carried out as follows :— 

A wooden chamber is fitted with a large number of shelves on which are placed 
trays containing litharge moistened with vinegar or dilute acetic acid. Carbon 
dioxide is passed in together with a little air and steam so as to keep the temperature 
at about 60° C. The paste is raked over from time to time in order to expose fresh 
surfaces to the action of the carbon dioxide. 

After a few weeks the whole of the lead is converted into white lead, which is 
ground and dried ready for use. 

Muilner’s Process.—This process consists in grinding together litharge, sodium 
chloride and water, whereby a mixture of an oxychloride of lead and sodium hydroxide 
is formed :— : 
4PbO+2NaCl-+-5H,O=PbCl,, 3PbO, 4H,0+2Na0H. 


WHITE PIGMENTS A5 


Carbon dioxide is then passed into the mixture, which converts it into white lead 
and sodium chloride thus :— 


3[PbCl,, 3PbO, 4H,0]+-6Na0H +800, 
—4[2PbCO,, Pb(OH),]-+11 H,O+6NaCl. 


Montgomery of St Lows has patented a process by means of which molten 
metallic lead is atomised by a jet of air, and passed into a closed chamber where it 
comes in contact with a spray of water. The resulting mixture is then carbonated 
in special cylinders and finely ground. 

Many other processes have been worked from time to time for the manufacture 
of white lead, such for instance as the various electrolytic processes, and those 
based on the action of alkaline carbonates on sulphates and acetates of lead. 
But as these have not come into general use there is not any necessity to 
describe them. 

Properties and Uses.—White lead is a basic carbonate of lead of the formula 
2PbCO,, Pb(OH),. It is a heavy white amorphous powder with a specific gravity 
of about 6-45. 

It is quite insoluble in water, but is readily dissolved by even dilute acids with 
violent effervescence due to the liberation of carbon dioxide. It is also soluble in 
hot alkalies such as caustic soda. On strongly igniting white lead it blackens ; 
the carbon dioxide is driven off leaving a residue of lead oxide. 

White lead becomes brown, grey, or black when exposed to the action of sul- 
phuretted hydrogen, ammonium sulphide, or any metallic sulphide soluble in water. 
The discoloration is due to the formation of lead sulphide; and if treated with a 
solution of hydrogen peroxide the colour can be restored again. 

The composition of white lead varies considerably according to the process by 
which it is made, and even white lead made by the same process shows slight 
variations. 

The percentage of carbon dioxide varies between 11 per cent. and 16 per cent. 
and the percentage of lead oxide between 83-75 and 86-75 per cent. 

The carbon dioxide in a well made white lead, as a rule, is round about 11:5 
per cent. ; and in those cases where it reaches 15 or 16 per cent. it is found that the 
white lead is deficient as regards body and opacity owing to excess of lead carbonate 
(PbCO,). 

White lead requires about 8 per cent. of linseed oil to grind it into paste form. 
It is marketed either in powder form or as a stiff paste ground in oil. 

On account of its valuable qualities as regards body, opacity, obscuring power, 
and because of its ease of working under the brush, it is used in enormous quantities 
as a paint for the protection of outside structures from the weathering influences 
of the atmosphere. 

The composition of white lead should be in the proportion of two parts of lead 
carbonate to one part of lead hydrate (PbOH),. The lead hydrate molecule has 
the property of tending to partially saponify the linseed oil in which the white lead 
is ground; and owing to this formation of a lead soap (lead linoleate) can be 


46 THE CHEMISTRY OF PAINTS 


ascribed the valuable elastic, durable, hard, and non-porous film given by lead white 
paints. 

White lead acts as a drier on the oil in which it is ground; hence paints con- 
taining white lead dry very hard and quickly. 

It is customary to add a trace of Prussian blue in the grinding of white lead in 
order to improve the colour; this is especially necessary in the case of the stack 
white leads, which are, as already mentioned, not such a good colour as those 
produced by the Chamber or French processes. 

Ground white lead is sold as genuine and also in three reduced qualities, viz. 
Nos. 1, 2, and 3, containing as a rule 25, 50, and 75 per cent. respectively of finest 
white barytes as an extender to reduce their price. 

The two main objections to the use of white lead, as we have already mentioned, 
are (1) the tendency for white lead paints to turn yellow and finally darken owing 
to the action of sulphur gases; and also to a lesser extent to the deposition of soot 
and black particles present in the air, especially noticeable in the neighbourhood 
of large towns ; and (2) its poisonous action producing what is known as lead colic. 


SCHEME FOR THE ANALYSIS OF WHITE LEAD 


1. Moisture—Weigh 5 gms. on a watch glass, place in an air oven, and keep 
at 105° C. till constant in weight. 

2. Carbon Droxide—Weigh out 2 gms. in a Schrotter apparatus (Fig. 9, p. 32), 
and treat with dilute nitric acid. Loss in weight equals CO,. Calculate to lead 
carbonate (PbCO,). 

3. Total Lead.—Take 1 gm. and boil in a covered beaker with 50 cc. of dilute 
hydrochloric acid till all is dissolved. Add 100 cc. of hot distilled water; filter 
if necessary and wash repeatedly with boiling water. Weigh any residue=Barytes 
(confirm by flame test). 

Evaporate to small bulk; add a little sulphuric acid and continue to evaporate 
till clouds of sulphur trioxide are evolved. Cool; add a little water and some 
alcohol. Leave for two hours, then filter through a Gooch crucible. Dry and weigh. 
Calculate lead sulphate to white lead, or to lead oxide. Subtract total lead oxide 
in the lead carbonate formed and calculate the difference to lead hydrate. 

4. Calcium.—This is rarely present, but if so, it may be estimated by pre- 
cipitating with ammonia and ammonium oxalate. 


SPECIFICATION FOR WHITE LEAD 


1. The white lead must be a pure basic carbonate of lead, of a good colour and 
soft in texture. 

2. It should contain between 25 and 33 per cent. of lead hydroxide Pb(OH)s. 

3. It should contain not more than 0-5 per cent. of moisture, or matter soluble 
in water. 

4, On reducing with ultramarine blue in the proportion of 10 parts of white 


WHITE PIGMENTS AT 


lead to 1 part blue, the resultant shade should be approximately equal to that given 
by the standard genuine white lead similarly treated. 

5. It should be wholly soluble in nitric acid, and the carbon dioxide evolved 
should be not less than 11 or more than 12-5 per cent. 


RESULTS oF ANALYSES OF VARIOUS WHITE LEADS 





Theoretical Composition. Stack. Chamber. American. 
per cent. per cent. per cent. per cent. 
Lead carbonate . . 68-95 
Lead hydroxide - 31-05 
100-00 
or 
Lead oxide : . 86°32 86-50 86:25 85-05 
Carbon dioxide . So bktoG 11-25 11-50 12-25 
Water : : : 2°32 2°25 2°25 2-70 














100-00 100-00 100-00 100-00 


Leap SULPHATE (PbSO,) 
(Non-poisonous White Lead, Bleisulfat.) 


Lead sulphate is obtained by adding sulphuric acid to a dilute solution of acetate 
of lead. The reaction may be expressed thus :— 


Pb(C,H,0,)>-+H,80,—PbS0,+2CH,COOH. 


The sugar of lead solution is prepared by the action of acetic acid and steam on 
granulated lead. The hot acetic acid liquors are continuously pumped on to large 
tubs filled with the granulated lead till it is all corroded away. To the solution of 
sugar of lead thus obtained sulphuric acid is added to precipitate out nearly all the 
lead that is present. 

The precipitated lead sulphate is well washed till neutral, then filter pressed 
and dried. It is often sold in the pulp form containing 20 per cent. of moisture. 

The acetic acid liberated may be used over again. 

A considerable amount of sulphate of lead comes on to the market in a pulp form 
known as “lead bottoms.” This is obtained as a by-product in the production 
of aluminium acetate from alum or sulphate of alumina and lead acetate, a mordant 
which is used in Turkey Red dyeing. 

The formation of the lead sulphate in this process may be expressed thus :— 


Properties and Uses.—Lead sulphate is whiter than white lead, but is very 
deficient in body and covering power; hence it is no use by itself as a pigment. 


A8 THE CHEMISTRY OF PAINTS 


It is largely used for mixing with lead chromes for making what is known as 
*‘ genuine ” lead chromes. 

It is not so heavy as white lead, and consequently requires more oil to grind 
it into paste form. Its specific gravity is 6-08. 

It is insoluble in water, and only with difficulty soluble in acids. Owing to its 
non-poisonous nature it is often offered by itself or in conjunction with other pigments 
as “ non-poisonous white lead” (Freeman’s White Lead). 

Sublimed White Lead. Sublumed Blue Lead.—The sublimed leads are manu- 
factured in America by various processes and are sold in many different grades. 
The average composition is as follows :— 


Sublimed White Lead. Sublimed Blue Lead. 


Lead sulphate : ; 75 48 
Lead oxide . A : 20 30 
Zinc oxide. , : 5 3 
Lead sulphite , ; er 8 
Lead sulphide : : os 11 

100 100 


In addition to these there have also been introduced in recent years in the 
English and American markets considerable quantities of what are known as 
“leaded zinc oxides.” These products are exclusively manufactured in America, 
and important claims are made for these pigments in connection with their durable 
wearing and non-chalking properties. Their composition also varies, but the 
following analyses of three of these products will indicate their general nature. 


(1) (2) (3) 


Lead sulphate . : : ; : 20 40 34:0 

Zine oxide . c é : é : 80 60 65:5 

Moisture. ‘ : ; : : a a 0-5 
100 100 100 


The sublimed leads are manufactured in America from a mixed ore consisting of 
galena (PbS) and zinc blende (ZnS). These ores are roasted in special furnaces in 
the presence of a hot blast of air whereby the zinc and lead sulphides are oxidised 
to lead sulphate, lead oxide and zinc oxide, which pass over as a fume or smoke into 
large brick chambers where it is collected. 


ZINC OXIDE 


(Zinc White, Chinese White, Zinkweiss, Blanc de Zinc, Blane de Neige.) 
Zinc white or zinc oxide has the composition represented by the formula ZnO. 
It is manufactured in enormous quantities, for use as a pigment, in England, Holland, 
France, Germany, the United States, and Belguim. 


WHITE PIGMENTS 49 


There are two processes in operation for the manufacture of this valuable 
pigment. First, the direct process from metallic zinc, and second, the indirect 
process in which zinc ores are used. 

The introduction of zinc oxide as a pigment to replace white lead was due to 
Courtois of Dijon, who in 1781 began the manufacture of zinc white. In a report 
made to the Institut de France in 1808 by Fourcroy, Bertholet and Vauguelin the 
use of zinc white, manufactured by Mollerat, is recommended as a substitute for 
white lead on account of its non-poisonous qualities, superior covering power, and 
its permanency and non-darkening properties. 

Leclaire about 1845 established a works at Courcelles on the Seine for the 
manufacture of zinc white on a considerable scale. He also prepared a drying 
oil by boiling linseed oil with manganese dioxide for use with his pigment, and 
thus opened up the way for the general use of zinc oxide as a pigment in place of 
white lead. 


MANUFACTURE 
1. The Direct Process 


The manutacture of zinc oxide by the direct process is carried out on the large 
scale in the following way :— 

Pure metallic zinc, obtained either by calcination of the ores or by electrolytic 
processes, is introduced into a number of retorts. These retorts are made either 
of cast-iron or of fire-clay, and are closed at one end, the other end opening out into 
a main flue which is connected with the condensation chambers. The retorts are 
built into a reverberatory furnace—as a rule about twenty retorts are used—arranged 
either in two rows one above the other or else back to back. 

After the retorts have been charged with the metallic zinc, and the covers 
luted on, they are brought to a white heat, causing the metallic zinc to be converted 
into volatile fumes. These fumes issuing out into the flue come into contact with 
a current of hot air and thereby ignite, giving off great clouds of white zinc oxide 
vapour, which is driven over into the collecting or condensation chambers. The 
zinc oxide is collected from time to time and packed into bags or casks ready for use. 


2. The Indirect Process 


This process is supposed to give a zinc oxide of greater denseness and opacity 
than that obtained by the direct process; but owing to the impurities, such as 
cadium, present in the natural zinc ores, special care is required in carrying it out, 
otherwise the colour of the zinc oxide produced would be seriously impaired. 

In this process, which is largely used in Holland, the zinc oxide is manufactured 
directly from the natural occurring zinc ores. 

The zinc ores, such as zinc blende (ZnS) and calamine (ZnCO;) are mixed with 
coal or coke and heated to a white heat either in earthenware retorts or else in the 
bed of a reverberatory furnace. The issuing fumes are ignited in the presence of 
a current of air whereby the metallic zinc burns to zine oxide, and this white smoke 
of zinc white thus formed is driven over to the collecting chambers. 


50 THE CHEMISTRY OF PAINTS 


In this process the zinc oxide that collects in the chambers nearest the furnace 
is of a greyish, coarse shade, due to the deposition of metallic zinc, dust, soot and 
other impurities, whilst the finest snow-white grades collect in the end chambers. 

The presence of cadmium in the zinc ores is deleterious to the colour of the 
zinc oxide formed, tending to give it a brownish hue; hence care must be taken 
to eliminate it. 

Properties and Uses.—Zinc oxide is a soft white tasteless and odourless powder. 
It is rather bulky, and requires about 18 per cent. of linseed oil to grind it into a 
paste. Its specific gravity is 5-6. 

It is quite insoluble in water, but readily soluble in dilute acids, also in alkaline 
solutions. 

It is quite permanent, and does not darken on exposure to sulphuretted 
hydrogen fumes ; it can be mixed with other pigments without change. On gently 
heating it turns yellow, but regains its colour on cooling. 

It is largely used in the manufacture of paints and enamels in place of white 
lead on account of its permanency and non-poisonous properties, especially for 
inside work. 

Its covering power is superior to that of white lead, but its obscuring power 
is nothing like so good. Further, zinc paints do not dry so readily, or give such 
hard and tough elastic films as those given by white lead, and their wearing 
properties are not so good. 

When exposed to severe atmospheric influences it is found that in course of time 
the zinc paints chalk and rub off, whilst lead paints under the same conditions are 
considerably more permanent. 

It is largely used both in oil and water by artists under the name of 
Chinese white. 

Zinc oxide rapidly darkens in the presence of alcohol on exposure to sunlight. 
This peculiar property, which appears to be little known, renders paints made on 
a zinc oxide basis unsuitable for painting compasses in which alcohol is used— 
e.g. airship compasses—unless the paint is covered with an insoluble varnish to 
protect it from the action of the alcohol. 

Zinc oxide is sold under the following marks, viz., White Seal, Green Seal, Red 
Seal, Yellow Seal, Grey Seal. The last-named contains metallic zinc. The White 
Seal and Green Seal zine oxides are remarkably pure, and contain, as a rule, over 
99 per cent. of zinc oxides. 


SCHEME FOR THE ANALYSIS OF ZINC OXIDES 


1. Insoluble.—Dissolve 1 gm. in dilute hydrochloric acid by gently warming. 
If there is any residue, filter off, wash and ignite. Test for barium sulphate 
and silica. 

2. Total Zinc.—Make up the zinc solution to 250 c.c., and pipette out 50 c.c. 
Add 25 c.c. of chloride solution (see below), together with 50 c.c. of distilled water. 
Boil up in a conical flask, and when just boiling add two to three drops of ferric 


WHITE PIGMENTS 51 


chloride solution (about 1 per cent.). Then proceed to titrate with standard solution 
of potassium ferrocyanide. 

At first a blue precipitate is formed, which after the neutral point is passed 
changes to a pale green. 

It is important that the solution should be kept as near to boiling-point as 
possible in order to ensure a fine end reaction; also that the flask be continually 
shaken while the titration is proceeding. 

It is also advisable to go a little past the neutral point, and titrate back with 
a standard solution of zinc chloride. Calculate to zinc oxide (ZnO). 

The chloride solution mentioned above is simply ammonium chloride and 
hydrochloric acid in water in the following proportions :— 


53-5 gms. NH,Cl, 
36-5 gms. HCl, 


and made up to 1 litre with distilled water. 

Alternatwe Method (using uranium nitrate as an outside indicator).—Make up 
a solution of potassium ferrocyanide containing 21-55 gms. per litre. Standardise 
thus :— 

Weigh out 0-2 gms. pure zinc ; dissolve in hydrochloric acid (1 : 2) in a 400 c.c. 
beaker. Dilute and make faintly alkaline with ammonia. Again acidify with 
hydrochloric acid and add 3 c.c. of conc. hydrochloric acid in excess. Dilute to 
250 c.cs. and heat to boiling-point. Titrate hot as follows :— 

Reserve about one-third of the zinc solution. Titrate the remainder by 
running in a few c.cs. at a time till a drop tested on a porcelain tile with a drop of 
15 per cent. uranium nitrate solution gives a brown coloration. Now add the 
greater part of the reserved portion, and titrate more cautiously until the end 
point is passed. Finally add the rest of the reserved quantity, rinsing the beaker 
with a large part of the solution from the titration vessel. 

Finish very carefully, testing after every addition of two drops. It is well 
in each test to take out several drops of the zinc solution when the end point 
is being approached. 

When a brown tinge appears on the indicator, note the burette reading and wait 
one or two minutes, and see that one of the earlier tests has not developed colour. 

The end point is always passed by a drop or two; correct the burette reading 
accordingly. Correct it also for the amount of ferrocyanide needed to give colour 
under the same conditions when no zinc is present (one drop as a rule). 

Roughly 1 c.c. of standard solution equals 0-005 gms. zinc or 0-006 gms. of 
zinc oxide. 

Now dissolve -5 gms. of the sample of zinc oxide under analysis in 50 c.cs. 
dilute hydrochloric acid, and proceed as given above. 

The above method for the volumetric estimation of zinc in zinc oxide depends 
on the formation of zinc ferrocyanide according to the following equation :— 


27nCl,++K ,FeCy,-+3H,0 =Zn,FeCy,+4KCl+3H,0. 


52 THE CHEMISTRY OF PAINTS 


The zinc oxide may also be estimated gravimetrically by precipitating either 
as the sulphide or carbonate of zinc and igniting to zinc oxide. 

3. Calcitum.—lf present may be estimated by precipitation with ammonia and 
ammonium oxalate after the removal of the zinc by ammonia and ammonium 
sulphide. 

4, Lead.—Dissolve 1 gm. in dilute hydrochloric acid (filter off any insoluble 
if necessary); evaporate nearly to dryness on a hot plate. Cool and add 25 c.cs. 
dilute sulphuric acid and evaporate again till sulphur trioxide fumes are evolved, 
showing that all the hydrochloric acid has been expelled. Cool; add 25 c.cs. cold 
water and 25 c.cs. alcohol, and leave for two hours to allow all the lead to precipitate 
out. Filter through a weighed Gooch crucible. Wash well with 50 per cent. alcohol 
till free. Dry and gently heat over a low Bunsen burner and weigh as lead sulphate. 


SPECIFICATION FOR ZINC OXIDE 


1. The zinc oxide must be a pure sublimed zinc oxide, and free from any 
adulterant or foreign matter. 

2. It must be of a pure white colour, and soft in texture. 

3. It must be free from metallic zinc and contain not less than 98 per cent. zinc 
oxide, or more than 1 per cent. of lead expressed as lead oxide. 

4. It should not contain more than 0-5 per cent. of moisture, or matter soluble 
in water. 

5. It must not darken on exposure to sulphuretted hydrogen. 

Note.—Sometimes a lead-free zinc oxide is required for special purposes such 
as for paints for lyddite shells. In this case it is customary to specify a zinc oxide 
containing not less than 99 per cent. of zinc oxide, and not more than 0-2 per cent. 
of lead or lead compounds calculated to metallic lead. 

The small traces of “soluble ”’ lead in these cases are estimated according to 
the official test as follows :— 

A weighed quantity of the sample is continuously shaken for one hour at room 
temperature with 1000 times its weight of 0-25 per cent. of hydrochloric acid. The 
mixture is allowed to stand for one hour, and is then filtered. The lead contained 
in an aliquot portion of the clear filtrate is then precipitated as lead sulphide and 
weighed as lead sulphate. 


LITHOPONE 


(Enamel White, Porcelain White, Charlton White, Orr’s White, Griffiths’ or 
Knight’s Patent Zinc White.) 


Lithopone is a white pigment consisting of a mixture of blanc-fixé and zinc 
sulphide. This pigment was first patented by Orr in 1874, and the manufactured 
product was called Zinkolith, or Orr’s Zinc White. 

The process for the manufacture of this pigment is still carried on at Orr’s 
Zinc White Company’s Works at Widnes, Lancashire. 


WHITE PIGMENTS 53 


White pigments of a similar composition were introduced by Griffiths in 1875 
and by Knight in 1876. 

Lithopone is now manufactured in immense quantities for use as a pigment in 
the paint trades as a non-poisonous substitute for white lead in Germany, Holland, 
Belgium, the United States and England. 

The process of manufacture varies considerably in the many different works 
engaged in the production of this extremely valuable white pigment, but the main 
essentials of the process are based upon the following reactions :— 

1. Barium sulphide is first prepared by calcining finely ground barytes (Heavy 
Spar BaSO,) with charcoal, coke or coal in retorts at a white heat; the calcined 
mass is then dropped into water and lixiviated to dissolve out the barium sulphide— 


BaSO,+4C=BaS+4CO. 


2. The next operation consists in making up a weak solution of zinc sulphate, 
care being taken to see that it is perfectly free from iron. This solution is run into 
the solution of barium sulphide with continual stirring till a slight excess of zinc 
sulphate remains over. The precipitate of barium sulphate and zinc sulphide thus 
formed is well washed by decantation till perfectly free, then filter-pressed and 
dried at about 50° C. 

The dried mixture thus obtained is of a greyish-white colour, and of a very 
harsh texture. 

The reaction that takes place may be expressed thus :— 


BaS+ZnSO,=BaSO,+ ZnS. 
eet 
Lithophone 


3. The crude dry lithopone is next calcined at a dull red heat in special 
furnaces, and the red-hot mass raked out into iron tanks containing cold water. 
This sudden cooling in cold water of the calcined material causes it to become softer 
in texture, and also makes it denser and thus have more body. 

The cooled mass is next thoroughly ground under water till perfectly fine ; 
it is then pressed and dried. 

An alternative method which is carried out in some works consists in pre- 
cipitating the barium sulphide with a solution of zinc chloride thus :— 


(1) BaS+ZnCl,=ZnS +BaCl,. 


A solution of zinc sulphate is next added whereby barium sulphate is precipitated 


thus :— 
(2) BaCl,+ZnSO,=BaSO,+ZnCl,. 


The zinc chloride thus set free can be used to precipitate more zinc sulphide 
by the fresh addition of barium sulphide addition, as in equation (1). 

The advantage of this process consists in the fact that the proportion of barium 
sulphate to zinc sulphide can be regulated at will according to the grade of lithopone 
desired. 

Properties and Uses.—Lithopone is of a good white colour and is soft in 


54 THE CHEMISTRY OF PAINTS 


texture. It has excellent body and density, although not equal to white lead in 
this respect. Its specific gravity is 4°3. 

It is non-poisonous, and on account of this, and also because its cost is only 
about half that of zinc oxide and white lead, it has gradually come more and more 
into favour as a pigment, till at the present time the yearly consumption is enormous. 

It requires about 12 per cent. of oil to grind it into a stiff paste. Itis largely used 
as the basis of many of the cheaper dark-tinted paints such as slate greys and so on. 

Lithopone is insoluble in water, but is readily attacked by even dilute acids, 
with evolution of sulphuretted hydrogen. 


ZnS +BaSO,+2HCl=BaSO,+ZnCl,+H.S. 
— 
Lithopone 


It is not affected by sulphur gases. Unfortunately lithopone has two serious 
defects, which greatly impede its still more extended use. The first is its insta- 
bility as regards light. In the presence of sunlight it rapidly darkens, gradually 
turning grey, then black. On leaving in the dark it regains its white colour. 

The second defect is that when this pigment is made up into paint form, and 
used for the protection of outside structures, it wears very badly, and after twelve 
months’ exposure chalks and flakes off. Moreover, in iron structures, owing to the 
decomposition of the zinc sulphide, acids are formed which cause corrosion. 

This darkening property of lithopones has been the subject of very much 
patient investigation by many chemists, and many patents have been taken out 
with the object of preparing lithopones fast to light. 

It is now supposed that the darkening of lithopones can be ascribed to the 
presence of a small proportion of chlorides, and several processes are now in 
operation whereby lithopones more or less fast to light are produced. 

Eibner (“‘Chemiker Zeitung,” February 1923) states that the well-known 
darkening action of sunlight on lithopone is due to phosphorescence of the ignited 
zinc sulphide, caused by the presence of impurities in the shape of small quantities 
of foreign metals. These react with the zinc sulphide in the presence of sunlight, 
forming coloured sulphides, which subsequently oxidise, thus restoring the original 
colour. ‘The presence of lead, manganese and copper causes the pigment rapidly 
to become grey ; iron, nickel and cobalt have the same effect, but the colour takes 
much longer to develop. Manganese alone produces brown tints; cadmium, 
yellowish tints; and thallium and antimony salts, first reddish tints, then a grey 
or black discoloration. Long ignition of the lithopone in the process of manu- 
facture results in a product containing up to 2 per cent. of zinc oxide, and this 
accelerates the rate of oxidation of the foreign metals to white or more feebly- 
coloured compounds, but does not prevent darkening first occurring. The latter 
effect is accelerated by the presence of water or chlorine compounds; the latter 
especially are objectionable, as they result in the impurities being converted into 
chlorides, which in the presence of light are quickly converted into sulphides, 
producing much greater discoloration than if chlorides are absent. Lithopone 
absolutely free from foreign metals shows no discoloration at all, even if chlorides 


WHITE PIGMENTS 55 


are present. A satisfactory purification of the zinc solution previous to treatment 
with barium sulphide is obtained by treating it with ammonia to dissolve the zinc 
hydroxide first precipitated, filtering and boiling with zinc dust. In this way 
iron, manganese, lead, cadmium, copper, thalium, nickel, and cobalt are completely 
removed, and the lithopone made from this solution is absolutely fast to light. 

Ostwald & Brauer, according to a German patent (D.R.P. 202709), conduct the 
calcination process in closed vessels, or in vessels through which inert gases free 
from oxygen are passed, and lixiviate the red hot mass in water which has been 
previously well boiled to remove all air. 

Bayer & Company’s process consists in treating the finished lithopone in water 
containing a small percentage of alkaline sulphate or chlorides through which an 
electric current is passed. 

Lithopone comes on to the market usually as 30 per cent. Red Seal Brand, 
the average composition of which, according to many analyses made by the 
author, is as follows :— 

German Red Seal Dutch Red Seal 








Lithopone. Lithopone. 
Barytes(BaSQ,) . : , : 69-92 70-10 
Zinc sulphide (ZnS) : ; : 29-51 26-60 
Zinc oxide (ZnO) . : 4 ; 0-57 3°30 
100-00 100-00 








Other brands which also come on to the market to a much lesser extent are :— 


Green Seal containing 40 per cent. ZnS 


29 99 9? 34 9 a, 
29 33 9) 32 33 o> 
White bE 39 26 39 9) 
Blue: .,, a 22 - < 
Yellow ,, se liane 3 


The covering power and body of lithopone vary according to the amount of 
zine sulphide they contain. The higher the contents of zinc sulphide the greater 
the body and covering power, and vice versa. 

In some of the poorer grades of lithopone finely ground natural barytes is 
mixed in place of the precipitated blanc-fixé made during the process, but this has 
serious disadvantages as regards the texture and body of the finished product. 

Sulfopone—A white pigment has been marketed under the name of sulfopone 
as an alternative to lithopone. It consists of a mixture of calcium sulphate and 
zinc sulphide. 


ANALYSIS OF LITHOPONE 


Moisture——(1) Heat 2 gms. at 105° C. till constant in weight. Loss in weight 


equals the moisture. 
(2) Barium Sulphate (BaSO,).—Boil 1 gm. with diluted hydrochloric acid 


E 


56 THE CHEMISTRY OF PAINTS 


till no more sulphuretted hydrogen is evolved. Filter, wash well and ignite. The 
residue equals the barium sulphate (BaSO,). 

Note.—If the lithopone is treated with dilute sulphuric acid in place of hydro- 
chloric acid the author finds that the weight of the residue (BaSO,) obtained is 
always 0°5 to 1 per cent. higher. This is due to the slight solubility of the barium 
sulphate in dilute hydrochloric acid. 

(3) Total Zinc.—Add slight excess of ammonia to the filtrate from the barium 
sulphate, then add hydrochloric acid till acid. Bring nearly to the boil and titrate 
with standard potassium ferrocyanide as described under zinc oxide (page 51). 

The zinc may also be estimated by precipitating the solution from the barytes 
with excess of soda carbonate (anhydrous) and igniting the zine carbonate thus 
obtained to zinc oxide. 

(4) Zine Sulphide (ZnS).—Boil 1 gm. with hot nitric acid to which a few 
crystals of potassium chlorate have been previously added, and evaporate down 
to small bulk. Dilute and add barium chloride solution. Filter, wash, and ignite. 
Equals barium sulphate. 


BaSO, x 0-1373=weight of sulphur. 
Calculate sulphur to zinc sulphide. 


An alternative method consists in fusing 1 gm. of the sample with 5 gms. of 
a mixture of potassium nitrate and potassium chlorate for one hour. Extract 
the fused mass with hot dilute nitric acid and precipitate as above. 

(5) Zone Oxide (Zn0). —Calculate this by subtracting the zinc found as zinc 
sulphide from the total zinc in (3) and calculating to zinc oxide. 

(6) Calevum. —Separate the zinc by ammonia and ammonium sulphide and 
precipitate with ammonium oxalate in the usual manner. Calculate to calcium 
sulphate. 


SPECIFICATION FOR LITHOPONE (30 per cent.) 


The lithopone must be of a good white colour and fine in texture, and free 
from coarse particles. 

It must consist of a mixture of approximately 30 per cent. sulphide of zinc 
and 70 per cent. of precipitated barytes. 

It must not darken on exposure to sulphuretted hydrogen o or on exposure to 
sunlight. 

It must contain not more than 0°5 per cent. of moisture or matter soluble 
in water. 


Tirantum WHITE 
(Titanium Dioxide (Ti0,).) 
Titanium was discovered in 1791 by the Rev. Wiliam Gregor while investigating 


the magnetic sand (menachanite) found in Menachan (Cornwall). He called this 
element “ menachin.” 


WHITE PIGMENTS 57 


It was subsequently investigated in 1795 by M. H. Klaproth, who found what 
he thought to be a new metal in rutile and called it titanium (derived from “ Titans,” 
the fabled giants of ancient mythology). In 1797 Klaproth proved that titanium 
was identical with the menachin of Gregor. 

Titanium is not found in nature free, but combined it occurs as the dioxide 
(TiO,) in three minerals, rutile, brookite, and anatase, each of which possesses 
different crystalline forms. 

Titanium also occurs widely distributed in the minerals ilmenite (FeTiQ,), 
titaniferous iron ore, and sphene or titanite (calcium titanium silicate) (CaTiSiO,), 
that is CaO, Ti0,, Si0,. 

Titanium white (TiO,) is manufactured for use as a white pigment from the 
mineral ilmenite, which, as stated above, is a compound of iron oxide and titanium 
dioxide (FeO,Ti0O,), vast deposits of which are found on the west coast of Norway. 

The manufacture of this white pigment is carried out by the Titan Co. of 
Norway according to the following process. 

Finely pulverised ilmenite is mixed with ordinary concentrated sulphuric acid. 
The mass is heated whereby a violent reaction between the acid and the ilmenite 
takes place under coagulation of the mass, thus transforming the titanium and iron 
contents of the ore into titanium and iron sulphates. 

The coagulated mass is afterwards dissolved in water and freed from undecom- 
posed minerals through a settling process. 

The clear solution containing the iron and titanium sulphates is afterwards 
heated to a boiling temperature by means of indirect steam which causes the titanium 
to precipitate in the form of titanium hydrates, chiefly meta-titanic acid. The 
titanium precipitates thus obtained are washed until free from iron. The pre- 
cipitate contains a small quantity of absorbed sulphuric acid, and small quantities 
of basic sulphates of titanium which are neutralised by the addition of barium 
carbonate. 

The neutralised precipitate is afterwards calcined to remove the water of 
hydration and to convert the titanium dioxide into a crypto- or micro-crystalline 
condition. 

This white pigment is marketed under the name of titanium white, and is 
essentially titanium dioxide (TiO,), containing only a minimum proportion of barium 
sulphate. 

Reduced titanium whites, or the so-called “‘ composite pigments,” are also 
manufactured and are prepared by precipitating the titanium dioxide on a barium 
sulphate base. 

The process for the manufacture of the composite pigments is broadly as 
follows :— 

Ilmenite is smelted in an electric furnace with fluxes whereby a titanium 
concentrate is produced, which is afterwards dissolved in sulphuric acid. This 
forms a solution of titanium sulphate comparatively free from iron, most of the 
iron having been eliminated in the smelting process. 

The titanium sulphate solution is mixed with blanc-fixe and the mass boiled 


58 THE CHEMISTRY OF PAINTS 


by direct steam, thereby precipitating titanium hydrates upon a base of blanc-fixé, 
so that a mutual absorption of the two compounds takes place. 

By subsequent calcination the amorphous precipitate is converted into the 
crypto-crystalline or micro-crystalline state, whereby the two compounds are so 
to say coalesced. 

After calcination the titanium pigment is very carefully pulverised and air- 
floated so as to yield a product of the highest possible fineness and uniformity. 

Properties and Uses.—Titanium white (TiO,) has a brilliant white colour and 
is extremely fine in texture. Its specific gravity ranges from 4-0 to 4:3. It requires 
about 23 per cent. of oil to grind it into a stiff paste. 

Titanium white is quite inert and is not affected either by heat, acid, or sulphur 
fumes. It is non-poisonous. Paints made with it are exceptionally durable on 
exposure and retain their colour under all conditions. 

The pigment has exceptional body and covering power, and paints made with 
pure titanium white have, bulk for bulk, nearly twice the opacity or obscuring power 
of paints made with pure white lead. 

Owing to its complete inertness it exerts no drying influence upon the oil or 
varnish with which it is ground, so that the paint film obtained on drying (on the 
addition of dryers) is rather soft and apt to pick up dust. 

This defect is entirely prevented by the addition of 10 to 25 per cent. of oxide 
of zinc which hardens the film, thus preventing discoloration by the accumulation 
of dust or dirt. 

The cost of titanium white—which is about twice that of zinc oxide or white 
lead—is a serious impediment to its more extended use in the paint industry, but 
there is little doubt that, provided its cost of production can be considerably reduced, 
it will come largely into use, and be a valuable addition to our present white 


pigments. 
ANTIMONY OXIDE 


(Antimony White.) 
White antimony oxide, or antimonious oxide (Sb,0,), has been introduced of 
recent years as a substitute for white lead on account of its non-darkening and non- 


poisonous properties. 
When metallic antimony is burnt in contact with air or oxygen the fumes evolved 
consist of antimonious oxide. 
The raw material used in the manufacture of antimony oxide is stibnite, or 
grey antimony (Sb,Ss). 
The naturally occurring stibnite, either alone or mixed with iron, is roasted 
in the presence of air whereby the antimony oxide thus formed is converted into 
a fume or vaporised, and collected in much the same manner as zinc oxide. 


Sb,8,+3Fe=28b+3FeS 
4Sb+30,=2S8b,03. 


When native antimony sulphide is dissolved in hydrochloric acid, sulphuretted 


WHITE PIGMENTS 59 


hydrogen is evolved, and antimony trichloride formed. If water is added to the 
antimony trichloride the oxychloride (SbOCI) is precipitated, and by prolonged 
digestion, this is transformed into antimonious oxide. 


SbCl,-+-H,O=SbOC1+2HCl 
28bOC]+H,0=Sb,0,-+2HCl. 


Algorath powder has the composition approximately of SbCl,+Sb,0s. 

Properties and Uses——Antimony oxide when carefully prepared for use as a 
pigment is of a pure white colour. 

Its specific gravity 1s about 5-4, which is approximately that of zinc oxide; it 
differs however from zinc oxide in that it requires only about 10 per cent. of oil to 
grind it into the form of a stiff paste. 

It is of a fine crystalline nature, and exceedingly soft and “ buttery ” in texture. 

Antimony oxide is very slightly soluble in water, but wholly soluble in hot 
concentrated hydrochloric acid. 

Antimony oxide paint films turn yellow in the presence of sulphuretted 
hydrogen, but on exposure to pure air and light regain their original colour. Under 
ordinary atmospheric conditions this oxide retains its colour better than white lead. 

On account of its non-toxic properties it is used as a substitute for white lead, 
especially in France, where, owing to the prohibition of the use of the latter material, 
very large quantities are brought into consumption. 

Antimony oxide differs from zinc oxide and white lead inasmuch as it is an 
acidic pigment, and also has no accelerating effect on the drying of linseed oil such 
as is the case with white lead. On account of its inert character it has, unlike zinc 
oxide, no thickening or “ feeding” action on varnishes. 

Paints made up from antimony oxide are rather slow drying, and tend to give 
soft films; this, as with titanium white, may be overcome by the addition of a 
percentage of zinc oxide. 

The opacity of antimony oxide paints is equal to that of lithopone ; and under 
weathering influences its durability has been shown to approximate to that of white 
lead. 

Tin Oxripe (Sn0,) 


Tin oxide or tin white is a white powder, which may be prepared by heating 
metallic tin in the air ; also by the action of nitric acid. 

If metallic tin is dissolved in concentrated nitric acid and poured into water, 
a dense heavy white powder of tin hydroxide is produced (Sn(OH),). 

Tin oxide is insoluble in water and acids, and is used for colouring glass (opal 
glass) and in vitreous enamels. 


CHAPTER VII 
THE YELLOW INORGANIC PIGMENTS 


(A) THE YELLOW EARTH COLOURS 


1. YELLow OcHRE, OcKER, CHINESE YELLOW 


Tue natural yellow ochres occur very widely distributed in various parts of the 
earth. The best known and purest varieties are the French, English and Spanish 
ochres. They owe their yellow colour to the fact that they contain hydrated ferrous 
oxide. 

Preparation.—The natural occurring crude ochres are prepared for use in the 
pigment industry by grinding and levigation, as by this means the coarser and 
heavier particles are separated from the lighter material. 

Levigation.—This process, which is largely used in the separation of the heavy 
and coarser silicious particles from the finer material, will be briefly described here 
as it is applicable to all the earth colours ; and although the oldest form of separation 
known, is still by far the simplest and cheapest method available. | 

The earth colours as they are dug up are emptied into huge wooden or stone 
tanks, built usually into the slope of a hill, mixed with water from a stream and 
stirred either by hand or mechanically. By this means the heavier and coarser 
particles separate to the bottom whence they are from time to time removed. The 
stream of water which is continually flowing in washes away the finer particles into 
two or three series of tanks (each series generally consisting of four or five tanks), 
each succeeding tank being larger than the previous one. In this way the first series 
of tanks is eventually completely filled with the muddy liquor, the last and largest 
tank containing the finest grades. The stream of water is now diverted to the 
second series of tanks and the same operation repeated whilst the first series is — 
settling out. 

After settlement the clear water is run off and the fine ochre is dug out 
and allowed to dry in the sun or by the aid of artificial heat in 12-20 feet 
long kilns. 

In more modern works the sludge is pumped out and filter pressed to remove 
the excess of water, and then dried. 

In some cases the earthy material receives a preliminary grinding under water 
in edge runners so as to grind out the heavier particles. It may be of interest to 
mention here that one of the French firms engaged in the ochre industry mine 

60 


YELLOW PIGMENTS 61 


100,000 tons of ochre annually, out of which only about 20,000 tons are suitable 
for the paint trade. 

Recently the Plauson colloid mill has been introduced, by means of which 
particles of colloidal fineness are produced by centrifugal force. 

This process will undoubtedly be largely used in the near future for the pro- 
duction of pigments which are required to be in a state of extremely fine division 
for use in the paint industries. 

The Plauson Colloid Mill (see Figs. 11 and 12) consists essentially of a strong 
circular cast-iron body. The body is double cased to provide for heating or cooling, 
and has suitable branches fitted with baffles for filling the machine with solids and 
liquids. 

In the lower part of the body there is a shaft which is designed to run at about 
3000 r.p.m. This revolving shaft has steel blades or beaters attached, which rotate 
between two sets of blades or anvils fixed to the body. 

Perforated baffle plates are arranged coaxially with the beater shaft to reduce 
needless friction of the material, openings being left for the material being treated. 

As liquid is necessary for the operation of the mill, dry grinding cannot be 
carried out. 

The chief grades of ochre which come on to the English market are :— 


(1) The French Ochres: Golden Ochre, J.F.L.S., J.F.L.E.S., J.F.L., J.C., ete. 
(2) Native Oxford Ochre, Stone Ochre. 

(3) Spanish Ochre and Italian Ochre. 

(4) Indian Ochres. 


Very often a poor coloured ochre is toned up by the addition of a little chrome 
yellow to improve its colour, and the author has even come across ochres to which 
a small percentage of yellow acid dyestuff has been added with the same object. 

Properties and Uses.—These pigments are soft in texture and extremely per- 
manent. Their covering power is moderately good. They are largely used as 
stainers and for graining work. On ignition they lose their water of combination 
and turn red, owing to the conversion of the yellow ferrous hydrate into ferric 
oxide. 

The specific gravity is about 2-80, but varies according to the grade, some 
grades being as high as 3-20. 

Strength.—To test the strength of an ochre reduce with ten times its weight 
of zinc oxide in linseed oil, and then compare with standard ochres similarly reduced. 
The percentage of iron is also a guide as to the strength and covering power of 
an ochre. 

Oil Absorption.—The amount of oil required to grind an ochre into a stiff paste 
is a factor of considerable importance in the manufacture of paints, and this should. 
always be determined when selecting an ochre, and the amount of oil found to be 
necessary checked against that of the standard ochre. 

Meihod.—Weigh out 1 gm. of the ochre on to a porcelain slab, and drop from 
a burette raw linseed oil on to same, working up the ochre all the while with a 


62 THE CHEMISTRY OF PAINTS 


palette knife. Stop adding the oil at the point where the ochre is just converted 
into paste form, and count the number of drops used. 

Specification.—The usual specification required for a good class of prepared 
ochre is as follows :— 

It must be of a good bright yellow colour and consist of a levigated natural 
hydrated silicate of aluminium containing iron compounds equal to not less than 
20 per cent. sesquioxide of iron (calculated as Fe,0,) and also contain not more than 
5 per cent. of calcium compounds in any form. Further, it must not contain more 
than 0-5 per cent. moisture. It must be perfectly fine and free from grit, and all 
pass through a 120-inch mesh sieve. 

It must be free from barium sulphate or any added matter, also from any 
brightners or toners such as chromate of lead or aniline dye-stufis. 

Analysis of Ochres.—The general scheme for the analysis of ochres is as 
follows :— 

Moisture.—Weigh out 5 gms. in a watch glass and heat at 105° C. for two hours. 
Loss equals the moisture. 

Combined Water.—Gently heat 2 gms. of the above dried sample in a weighed 
platinum crucible over a slow bunsen flame till constant. The ochre turns red 
and the loss in weight gives the combined water. 

Barytes and Silica.—Take 1 gm. of the ochre and boil up on a hot plate with 
100 c.c. conc. hydrochloric acid. Evaporate to dryness to render the silica insoluble. 
Add more hydrochloric acid and again evaporate down to small bulk. Filter off 
the insoluble matter, wash residue (which should be white, showing absence of iron), 
and ignite gently. The residue should consist of silica only. Test for barytes with 
the platinum wire ; if present it is an adulterant, and may be estimated by removing 
the silica by treating with hydrofluoric acid in the usual way. 

Lead.—Dilute well and pass in hydrogen sulphide. A black precipitate indi- 
cates lead. Filter off, wash, dissolve, add sulphuric acid (H,SO,) and weigh as lead 
sulphate and calculate to chromate of lead (see Chromed Ochres). Boil, filtrate 
to remove hydrogen sulphide, add ammonia. Filter and wash the precipitate well. 

Ferric Oxide.—Dissolve the filtrate in hydrochloric acid, make up to 250 c.c., 
and estimate the iron in 50 c.c. of this solution with standard bichromate of soda 
in the usual way. 

Alumina.—Pipette out another 50 c.c. and estimate alumina and iron by re- 
precipitating, ignite, weigh and calculate. The difference equals Al,O;. If lead 
is present the chromium must be separately estimated. 

Calctum.—The calcium in the filtrate is estimated from the iron precipitate 
by precipitation with ammonia and ammonium oxalate, and calculated either to 
carbonate or sulphate of calcium. 

Magnesium.—The magnesium is estimated as magnesium pyrophosphate. 
Carbon dioxide is estimated by treating 1 gm. in the ‘Schrétter apparatus, and 
sulphuric acid is estimated by precipitation with barium chloride. Calculate to 
carbonate and sulphate of lime. 

The following typical analyses (by the author unless otherwise stated) will 


(AGIA MOVG) TH GIOTION NosavIg—'ZI ‘slg ‘(MAIA LNOUT) TH GIOTIOQ NosavIg—'TT ‘OL 





a 





YELLOW PIGMENTS 63 


indicate the general composition of the ochres which are placed on the market in 











this country :— 

(1) Ochre, French J.F.L.S. (2) French J.C. Ochre. 
Moisture ; . 0-50 percent. Moisture. : . 0-70 per cent. 
Comb. water . . 8-90 Me Comb. water ; . 9-20 be 
Silica (SiO,) . . 52-00 ,, Silica (SiO,) 2 RE ay erate 
Ferric oxide (Fe,0,) 22-50 _,, Ferric oxide (Fe,0,) . 12°50 _,, 
Alumina (Al,0,) . 12-70 - Alumina (Al,O5)_ . . 8-50 ; 
Lime (CaO) . “oss tear Lime (CaO) . Age Fev es 
Undetermined. MAD — Undetermined ; ree OY, a 

100-00 100-00 
(3) French Prepared Ochre (G. H. Hurst). (4) Stone Ochre. 
Water, hygroscopic. 1-80 percent. | Water, hygroscopic . 0-50 per cent. 
Water, comb. . ee 9-20-55; Water, comb. : « 20 se 
Silica (Si0,)_ . OO: 5, Silica (Si0,) : eA en 
Alumina (Al,0,) . 13°75 ,, Barytes (BaSQO,) ~ PEO 
Ferric oxide (Fe,03) 20.73 _,, Ferric oxide (Fe,O;) . 9:40 ,, 
Calcium oxide (CaO) 0-19 i, Calcium carbonate (CaCO,) 28-40 _,, 

99-67 98-40 








Note.—This analysis of the stone ochre shows that it is not a genuine ochre, 
but has been adulterated largely by the addition of barytes and Paris white. 





(5) Extra Strong Bright Golden Ochre. (6) Spanish Ochre. 

Moisture . . . 2-10 percent. Loss onignition . . 6-87 per cent. 

Loss on ignition. . 11:20 ,, Silica (Si0,) . : eed BE lee 

Silica (Si0,)_ . . 52-30 . Ferric oxide (Fe,05) . 56-05 is 

Ferric oxide (Fe,0;) 30:40 __,, Alumina (Al,O5)_ . Og oi he he 

Alumina (Al,0,) . 4:00 ,, Calcium carb. (CaCO,) . 18-93 __,, 
Magnesium oxide (MgO). 1-10 ,, 

100-00 100-00 








(2) Raw Sienna, TERRA DI SIENA 


The siennas are not so widely distributed as the ochres, to which they have a 
certain resemblance. The chief source of supply of this valuable pigment is Italy, 
from which country by far away the best grades come. A certain amount is also 
obtained from Germany and America. 

Preparation.—By grinding and levigation in a similar manner to that described 
under Ochres. 

Properties and Uses.—Raw siennas have a deeper yellowish tone than the 
ochres. Their colour varies slightly according to the locality from which they 
are obtained. They are exceedingly transparent, and on this account are chiefly 
employed as stainers and for graining work. 

In selecting a sienna the undertone and transparency should not be overlooked. 


64 THE CHEMISTRY OF PAINTS 


Those that are “muddy” should be rejected, and only those grades should be 
accepted which are bright, transparent and clean on reduction. 

Analysis.—See under Ochres. 

The following analysis of an Italian and a German prepared raw sienna by 
the author will give a clear idea as to their composition :— 


Italian Raw Sienna, Ex G. 
1-20 per cent. 


German Raw Sienna, Ex S. 
0-70 per cent. 


Moisture 

Loss on ignition 12-50 
Silica (Si0,) 11-50 
Ferric oxide (Fe,03). 70-40 
Alumina (A1,05) 2-00 
Manganese dioxide . 0-70 


Calcium oxide (CaO) 2-20 
100-00 





Moisture 
Loss on ignition 20-40 
Silica (Si0,) . : 9-70 
Ferric oxide (Fe,05) 55-40 
Alumina (A1,0s) 8-00 
Manganese dioxide 0-30 
Calcium sulphate . 5-00 
100-00 





Specification.—The raw sienna must be a finely levigated natural earth colour 
in a fine state of sub-division, and free from any coarse particles. It must ccntain 
not less than 50 per cent. of iron (calculated as Fe,O,). It must also contain not 
more than 1-5 per cent. of moisture. It should be free from any added materials 
such as barytes, silica, Paris white, terra alba, etc. 

Burnt Sienna is obtained by calcining the raw sienna at a low temperature 
till the desired shade is produced. 

Properties and Uses.—Burnt sienna possesses a deep orange red colour, with a 
blood-red undertone. It is a beautiful transparent colour, and is very largely used 
as a stainer. Burnt siennas heavily reduced with silica and coloured with magenta 
to give them a rich undertone are frequently offered on the market. 

Strength Test.—The strength test of both raw and burnt sienna is carried out 
by reducing by 1 : 10 with zinc oxide in linseed oil. 

Specification.—See Raw Sienna. 

The following analyses, by the author, of an Italian and a German raw sienna, 
made after calcining, will indicate the changes the raw materials undergo :— 


Italian Burnt Sienna, Ex G. 
Moisture 


1 German Burnt Sienna, Ex S. 
Moisture -25 per cent. = 
8-80 per cent. 


Loss on ignition . 2UOo eg Loss on ignition 

Silica (Si0,) 13-55, Silica (Si0,) . ; 20:00 ss, 

Ferric oxide (Fe,O5) TOE as Ferric oxide (Fe,05) 65:05 sé, 

Aluminium oxide (Al,03) 1:58 _,, Aluminium oxide . §20 

Manganese dioxide. Fi 9 baled la i Manganese dioxide : A. 

Calcium oxide (CaO) . 1:99 _,, Calcium sulphate . t es 
99-55 100-00 








1 Note.—This German sienna was one of the best the author has ever come 
across. It had great strength and transparency, and the undertone was of a deep 
blood-red colour. 


YELLOW PIGMENTS 65 


(B) THE YELLOW INORGANIC CHEMICAL COLOURS 


1. CoRoME YELLOW 
(Chromate of Lead, Chromgelb, Jaune de Chrome.) 


This group of colours. commonly known as the “ Chromes,” is by far away 


the most important of the yellow pigment colours at the disposal of the paint 
manufacturer. Their value is due not only to their remarkably good body and 
covering power, but also to the fact that by their aid an immense range of bright 
shades can be obtained, varying, according to the method employed in their manu- 
facture, from the palest yellow (Primrose Chrome) to the deepest red shade (Derby 
Red or Persian Red). 

Moreover, in conjunction with Brunswick blues they give a wonderful variety 
of strong bright greens known as the Brunswick greens, which are manufactured 
in enormous quantities at the present time. 

The various chrome substitutes made from synthetic dyestuffs which have 
been placed on the market have not been able to take the place of the “ Chromes ” 
to any appreciable extent on account of their high price and lack of body. 

The Hansa yellows and similar types of synthetic colours (see Lakes and Lake 
Pigments, Chapter XIII.), in consequence of their great stability and permanency, 
will, no doubt, in course of time come more and more into favour as chrome 
substitutes, provided their cost of production can be reduced so as to put them 
on to a competitive basis with the ‘ Chromes.” 

Manufacture of Chrome Yellow.—lf a cold dilute solution of chromate or 
bichromate of potash or soda is run into a cold solution of a soluble lead salt such 
as nitrate or acetate of lead, pale bright yellow precipitate of chromate of lead 
is produced according to the following equation :— 


(a) Pb(NO,).+-K,Cr0,=PbCrO, +2KNO3. 


If this yellow precipitate of chromate of lead is next vigorously boiled with an 
alkali such as caustic soda or lime, a basic chromate of lead is produced thus :— 


(6) 2PbCrO,+2NaO0H=PbCrO,.Pb(OH),+Na,CrO,. 


On these two simple reactions the whole manufacture of chromes is based. 
The raw materials used by the colour manufacturer in the production of his 
chromes are :— 

(1) Bichromates of soda and potash. 
(2) Nitrate and acetate of lead. 


In the early days of the manufacture of chromes it was necessary, owing to 
their being no bichromates on the market, for the colour maker to manufacture 
his own bichromate of potash from chrome iron-stone (FeCr,0,), and this he did 
by fusion in a reverberatory furnace with potassium nitrate and subsequent 
lixiviation with water containing sulphuric acid. This has now fallen completely 
into disuse, as the colour manufacturer finds it more economical and convenient 


66 THE CHEMISTRY OF PAINTS 










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NY 


YELLOW PIGMENTS 67 


to obtain his supply of bichromates of potash and soda from the chemical works 
directly engaged in the manufacture of these products. 

Colour House Plant—The modern plant used by the colour maker in the 
production of his chromes will be described in some detail, as the same plant may 
also be used for the manufacture of Prussian blue, lake colours, greens, etc. 

The first essential in the manufacture of colours is that the colour house 
should have a plentiful supply of pure soft water. The presence in the water of 
lime, and especially of iron, is extremely deleterious to the bright shades which it is 
the aim of the colour maker to produce. The presence of sulphates and chlorides 
is also very objectionable if present in more than minute quantities. A plentiful 
supply of boiling water and steam must also be at hand. 

The colour house, a plan and elevation of which is shown in Figs. 13 and 14, 


is generally arranged in two storeys. 
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(see Fig. 15) having a capacity of mi 
TA 


1000 gallons or more according to 
i 


the sizes of the batches of colour a 
























ero 














that are going to be produced at 
one “striking” or precipitation. 

















ATT ATA 











These vats are about 5 feet high 
-and are provided with mechanical 
stirrers (Fig 16), the labour of hand- 
stirring being thereby eliminated. 
In addition the vats are provided 
with a series of pegs a, b, c, which 
can be removed at will; these are 
used for drawing off the top liquor 













mM 


te Mi 


















Fig. 15.—PREcrerraTion VAT. 


as the precipitate settles down. 

On the top storey, which is often simply a gallery running round the colour 
house, are placed two or three dissolving tubs of smaller capacity, say about 
250 gallons, each provided with three pipes to supply (1) hot water, (2) steam, 
(3) cold water. The bottom of the dissolving tubs are provided with a large tap 
fitted with a movable strainer. By means of this tap and strainer the contents 
of the dissolving tubs can be emptied at practically any speed according to the 
requirements of the particular colour or shade that is being made. Also at the 
same time the strainers will remove any undissolved particles or impurities that 
may be present. By means of a long wooden channel the contents of these vats 
can be run off into any of the receptacles below at will. 

The colour formed in the “ striking” or precipitating vats, after washing free 
from all insoluble matter, is pumped out through a filter press (see Figs. 17 and 17a) 
and pressed till all the excess of water is removed. In the case of small batches 
of colour these may be emptied by hand on to cloth strainers, but this is a slow 


68 THE CHEMISTRY OF PAINTS 


and cumbersome method. The colour is then removed to the drying-room or 
vacuum stoves. 

The Drying of Pigments——The drying-room or stove consists of a large brick 
chamber with solid walls and two doors, the latter of which are of course kept 
closed during the drying operation. The chamber is fitted up with a convenient 
series of racks or shelves about 2 feet apart and reaching to the top of the stove ; 
on these are placed the trays, which may be made of wood, iron or aluminium. 
Space is left between each series of racks to allow the men room for filling and 
emptying the stove. In addition the chamber is fitted with an electric fan, and 
a wet and dry bulk thermometer so that the humidity and the amount of air 
passing through may be regu- 
lated to ensure that the maxi- 
mum efficiency in drying is 
obtained. 

The heating is arranged 
either by a series of steam 
pipes or else by a fire with 
flues leading round the stoves. 
Very great care must be 
taken to see that the tempera- 
ture of the stove is carefully 
regulated, as any overheating 
would result in whole batches 
of the more delicate colours 
being spoilt. The tempera- 
ture of the stove varies from 
about 100° F. to 150° F. 
according to the position of 
the trays from the source of 
the heat. 

Many of the more per- 
manent colours can be dried more expeditiously by the aid of the vacuum stove. 
The illustration (see Fig. 18) shows a complete Scott vacuum drying installation 
which consists of a cast-iron chamber built up of heavily reinforced plates, 
bolted together on machined flanges. To the front of this chamber is fitted a 
cast-iron door carried on an overhead steel rail on roller bearing arranged so 
that the door can be moved easily into and out of place. The door has a 
square section rubber joint carried in undercut grooves and is held in place 
by steel swing bolts with quick-fitting handle nuts. Inside the chamber are 
arranged a number of steam-heated coil shelves. Each shelf consists of a single 
length of tubing very closely pitched and arranged with inlet and outlet branches 
which pass through the back of the stove and are connected into external steam 
and drain headers by means of unions and special flanged nuts, the whole being 
arranged so that the vacuum joint is distinct from the steam joint and there is no 



















a 
SS) 
f, 

ish 





Fic. 16.—PREcIrITATION VAT SHOWING STIRRERS. 





Fic. 17.—Twer.ve-cHAMBER WoopeEen Fitter Press FoR CoLtours; FLUSH PLATE AND DISTANCE 
FRAME Type; Puatses 28 In. By 21 In. THROUGH EXTRACTION WASHING ARRANGEMENT. 
PLATES FITTED wWitH LigNum Vitam Cocks. 


{ 

TESTE bo hdid dndhs re 
bE Shh 
Lee ed Ghee eS eSSSSSSS es. 


AEALLLA 


% 





Fic. 174.—Fitter PREss FoR CoLours; 25-IncH SQUARE D TypE wirH 30 CHAMBERS. 
(S. H. Johnson & Co., Ltd.) 


” 





YELLOW PIGMENTS 69 


possibility of steam leaking into the vacuum chamber. In other words, any steam 
leak is into the atmosphere and not into the stove. It is quickly detected, and 
it is possible to attend to either the steam or vacuum joint without removing the 
shelf. These coil shelves are reinforced and stiffened in a special manner which 
prevents the movement of the individual pipes when trays are slid into and out 
of position. In addition this reinforcement stiffens the whole shelf. 

In addition to the drying shelves a top heating coil for keeping hot the top 
of the chamber is provided, thus preventing condensation at this point, with a 
resulting slowing down of the drying on the top shelf. 

Vapour is led from the chamber through the vapour pipe shown and enters 
a horizontal two-flow condenser (tubular) arranged to give two passages for both 
the vapour and the condensing water. The condenser is made with contact parts 
to suit the particular liquid or vapours to be dealt with, and the condensed vapour 
is concentrated into a drip pipe projecting into the water receiver shown under 
the condenser. The water receiver is generally in mild steel, but sometimes in 
cast iron or copper. The internal drip pipe is kept under observation through the 
round light and sight glasses arranged near the top of the receiver. This enables 
the progress of the drying operation to be determined, as, of course, towards the 
end of the drying there is very little condensed solvent issuing from the drip pipe. 
This receiver is also fitted with gauge glass and fittings, discharge cock and air 
connection to vacuum pump. 

The receiver is made large enough to take the whole of the condensed steam 
or solvent in a charge of the stove. The condensed liquid is stored in the receiver 
until the end of the drying operation, and is run away to store or waste when the 
vacuum on the plant is broken and the door opened. 

The vacuum pump shown behind the receiver is of the vertical double-acting slide 
valve type, fitted with a special form of slide valve with transfer ports, designed to 
empty the clearance space at the end of the compression stroke into the suction side 
of the machine just after this has been closed from the vacuum space. . In this way 
the volumetric capacity of the air pump is very materially increased, particularly at 
the higher vacuums, and it is also possible to provide a higher vacuum by this means. 

Illustration (Fig. 20) shows the method of filing vacuum drying stove. The 
man is seen proceeding to place the trays containing the material to be dried into 
place. These trays—which can be of black steel, tinned iron, copper, aluminium, 
etc.—are arranged to come either directly on to the steam-heated surface, or in 
other cases are carried on runners clear of the surface. Usually a double set of 
trays are in use, one in the stove while the other is being discharged of the dry 
product and refilled with the wet material. 

Illustration (Fig. 19) shows the double receivers, condenser and vacuum pump 
for vacuum drying stove. 

This digression into the lay-out of a modern colour works, and the methods in 
vogue for the production of the prepared and dried pigments, will enable the 
manufacture of the various chrome yellows, so largely in demand at the present 
time, to be better understood. 


70 THE CHEMISTRY OF PAINTS 


The chrome yellows may appropriately be considered under the following 
shades, examples of the production of which will be given :— 

1. Primrose chrome. 3. Middle chrome. 
2. Lemon chrome. 4. Orange chrome. 

Chrome red (Persian red, Derby red, etc.) will also be, for convenience, con- 
sidered in this chapter, as it is a basic chromate of lead and naturally falls under 
this group. 

The chromes come on to the market as pure chromes and also as genuine 
chromes. They are also sold as reduced chromes Nos. 1, 2 and 3, the reduction in 
this case being obtained by the addition of terra alba. The genuine chromes are 
pure chromes to which a percentage (about 30 per cent.) of lead bottoms (sulphate 
of lead, PbSO,) has been added. 


1. Primrose CHROME 


This is the palest chrome on the market, and to obtain this exquisite delicate 
shade special care must be taken, as will now be described. 

If a dilute solution of lead nitrate is run into a dilute solution of potassium 
chromate or bichromate, according to the equivalent proportions calculated from 
the equation given above, a pale yellow precipitate is formed. On washing and 
drying out this precipitate, however, a deep shade of chrome yellow is obtained 
—due to the instability and lability to change colour of the chrome so produced. 
To overcome this lack of stability it has been found by experience that the palest 
chromes can only be obtained under the following conditions :—(1) The reacting 
solutions must be very dilute. (2) The temperature must not rise above 80° F. 
during the whole of the reaction. (3) An excess of soluble neutral or acid lead salt 
must be present. (4) The chrome must be precipitated in conjunction with sulphate 
of lead whereby a sulpho-chromate of lead is formed, which has much more stability 
and permanency as regards change compared with the normal lead chromate. 

The following examples will illustrate the method and proportions to be used 
so as to produce chromes of a delicate primrose shade :— 


Process A. Process B. 
Bichromate of soda . : . T4lbs. Bichromate of soda : . 100 Ibs. 
Alum=s ; : : . . 112 ,, Soda ash : : ; moms 9). 
Glauber salts . : : . 112 ,,, Glauber salts . ; ; > a ee 
Common salt . " ; . DOs, oy ele : : ; ; . tere 
Lead nitrate . : : . 350 ,, Lead nitrate . : : . 340 ,, 
Yield : ‘ Job te. Yield i * 240 


Process A.—Dissolve the bichromate of soda (or potash) in the dissolving vat 
in about fifty times its weight of water; add the alum and stir occasionally till all 
is dissolved. If hot water is used the solution must be allowed to cool down to 
75°-80° F. The Glauber salt and common salt are next dissolved in another 
dissolving vat in about fifty times their weight of cold water. 


SCOTT VACUUM SibVE ‘ 


ce) 





Fic. 18.—Vacuum Dryine Stove. (George Scott & Son, Ltd.) 


aria ams  pn 





YELLOW PIGMENTS 71 


The nitrate of lead is dissolved in the precipitating vat in fifty times its weight 
of cold water. The stirrers are now set going in the large precipitating vat, and 
the contents of the two dissolving vats slowly run in, with constant stirring. A 
precipitate of primrose chrome is formed. After all the contents of the dissolving 
tubs have been emptied and washed out stirring is stopped, and the precipitate 
of primrose chrome allowed to settle down. After complete settlement (about 
twelve hours) the mother liquor is run off by knocking out the plugs in the side 
of the vat as low down as possible without disturbing the chrome. The large vat 
is then filled up with cold water, stirred well, and allowed to settle down. 

The pale yellow precipitate is washed three or four times by decantation, till 
neutral, and then pumped out through the filter press, and dried at a low 
temperature. 

Process B.—In process B the soda ash is dissolved in the bichromate 
solution. Effervescence takes place owing to the evolution of carbon dioxide 
and the bichromate is converted into the normal chromate according to the 
following equation :— 


Na,CrO,-+Na,CO,—Na,CrO,+CO,. 


The process is otherwise carried out as in Example A. 

Genuine Primrose Chrome and Reduced Chromes.—If a genuine primrose chrome 
is required then all that is necessary is to add the required amount of precipitated 
pulp sulphate of lead or lead bottoms (see Chapter VI.), to the precipitated chrome 
just after it has been struck. 

This addition of sulphate of lead is also often done in the dry way; that is, 
the dried chrome is runnered in an edge runner or chaser (see Fig. 3) with the 
required amount of sulphate of lead until completely incorporated. The reduced 
grades of the chrome are obtained by adding the various amounts of terra alba 
(Paris white cannot be used as it tends to redden the shade of the chrome) according 
to the quantity required in Nos. 1, 2 or 3 chrome. 

Pure primrose chrome is naturally one of the weakest of the chromes on account 
of the large amount of precipitated sulphate of lead that it contains. 


2. Pure Lemon CHROME 


This shade of chrome is produced in the cold in precisely the same manner as 
described under primrose chrome, the only difference being that the salt is omitted, 
and the proportion of alum and Glauber salts very considerably reduced. In this 
way the proportion of the normal chromate of lead to the alumina and sulphate of 
lead is very considerably increased. The alum also may be left out and its place 
taken by its equivalent of Glauber salts. This is usually done, as the Glauber salts 
are considerably cheaper than alum. On the other hand, the presence of a small 
proportion of alumina in a chrome has a very beneficial effect, tending to give softer 
and brighter tones. 

The proportions given in the following examples will give a general indication 
as to how the lemon chromes are best produced. 


F 


72 THE CHEMISTRY OF PAINTS 


Examples— A, B. 
Bichromate of soda or potash . 112 lbs. Bichromate soda . . 100 lbs. 
Glauber salts : : ; 56 ,, Soda ash : : : alone 
Alum . : : : : 28 ,,  Glaubersalts . : é 60 3 
Lead nitrate or acetate . : 336 ,,  lLeadnitrate . ; : 300 ,, 
Yield ; : : PALS Trem Yield : , ol Seas 


As a general rule the bichromate of soda is always used in preference to 
bichromate of potash on account of the latter salt being more expensive. 

The manufacturer in the case of lemon chrome has the choice of using either 
the acetate or nitrate of lead, according to which is more convenient. 

It must, of course, be understood that each manufacturer has his own particular 
formula for producing the various chromes which give him the particular shade 
he requires, and which is the result of a long series of experiments and practical 
observations, taking into account such factors as dilution, temperature, rate of 
precipitation, and so on. 

The examples given above are only to be taken as types which may be modified 
very considerably, always, of course, remembering that to produce yellow shades 
of chromes it is necessary to have excess of lead salts, and also that the sulphate 
of lead must be precipitated along with the chrome so that the stable sulpho-chromate 
is produced. In addition to this, in order to get the brightest and palest shades, it 
is necessary to work with cold dilute solutions. 

Genuine Lemon Chrome and Reduced Lemon Chrome.—These chromes are 
obtained, as in the case of the genuine primrose chromes, by the mechanical addition 
of lead sulphate, or in the case of the Nos. 1, 2 and 3 lemon chromes by the addition 
of terra alba. 


3. Pure MippLe CHRromMEs 

Pure middle -chrome is practically pure normal chromate of lead, only a small 
proportion of sulphate of lead being precipitated along with the chrome. On this 
account it possesses by far away the greatest body and covering power of all the 
chromes. 

In the manufacture of this chrome the solutions used are considerably stronger 
(1-20) than in the case of the paler chromes ; also the temperature of precipitation 
is about 200 F. 

The proportion given in the following examples will show the method in use 
for the manufacture of this chrome. 


Examples— A, B. 
Bichromate of soda : ; . 601bs. Bichromate soda : . 100 Ibs. 
Glauber salts : 4 5 . -10 52 Aloe : . tt See A 
Lead acetate : ; 4 . 8b ,, * Lead nitrates ; yPhIOs 


Pulp white lead ‘ LU Lee 


er 


Strike at about 200° F. yield . eee iy Yield 2 Rene YS S; 

















Fig. 19.—Vacuum Dryine STOVE SHOWING THE DOUBLE RECEIVERS, 
CONDENSERS AND VAcuuM Pump. 





Fic. 20.—ILLustrRATION SHOWING MeETHOD OF FILLING VACUUM 
Dryine Stove. 





YELLOW PIGMENTS 73 


In Example B the white lead pulp is mixed in the precipitation vat 
with the hot solution of the lead nitrate, and the hot bichrome run in, 
stirring well. 

Genuine Middle Chrome and Reduced Middle Chromes.—Genuine middle chrome 
is produced by the addition of sulphate of lead to the pure middle as in the case 
of the primrose and the lemon chromes. 

Sometimes white lead is present, due to the fact that an excess of white lead 
is used in its manufacture, and a certain proportion remains over unchanged. 

The reduced grades contain terra alba in varying amounts. 


4. PurE ORANGE CHROME 


Orange chrome is a basic chromate of lead (PbCrO,Pb(OH,)), associated with 
a certain proportion of the normal chromate of lead. 

The formation of this pigment may be divided into stages. In the first stage, 
the normal chromate of lead (PbCrO,) is formed; the second stage consists in 
boiling this with an alkali such as caustic soda or lime, by means of which part of 
the normal chromate is converted into a basic chromate of lead according to the 
equation (a) and (6) given at the commencement of this section (page 65). 

On the manufacturing scale a solution of lead nitrate, or basic sugar of lead 
(obtained by dissolving litharge in a hot solution of lead acetate), is run into the 
hot solution of sodium bichromate or vice versa. Steam is passed through and the 
whole mass boiled and stirred for two or three hours, with the addition of a small 
quantity of milk of lime or caustic soda to produce the desired shade. 

Test samples are drawn off from time to time and dried out, and when the right 
shade is obtained the boiling is stopped. After settlement the mother liquor is 
drawn off and the chrome well washed to remove all excess of alkali and soluble 
salts. If this is not carefully done the chrome will spot or blur when made up into 
a paint with oil. The chrome is then filter-pressed and dried. 

The examples given below will illustrate the proportions used in the manu- 
facturing scale :— 


A. (Pale Orange). B. (Deep Orange). 
Soda dichromate . , 100 lbs. Soda dichromate 4 eaaee LOO. ba 
Lead nitrate x f 150 ,, Basic sugar of lead. 2 ee Le 
Pulplead . E , Loy Lime ; : : : 23°; 
Caustic soda ; : 25%, 

eC a Sure LOge Yield : : : 76 : 


Properties—The orange chromes vary in shade from a pale orange to an 
extra deep orange; they are soft in texture and have excellent body and 


covering power. 
Genuine Orange Chrome is produced by adding red lead to the pure orange 


chrome ; the reduced varieties contain terra alba, barytes, etc. 


74 THE CHEMISTRY OF PAINTS 


5. Pure Curome Rep (Persian Rep, Dersy Rep, Cuinese Rep) 


This pigment, although a red pigment, is practically a pure basic chromate of 
lead (PbCrO,Pb(OH),) and may therefore be conveniently described here. 

It is a bright brick-red powder of a somewhat crystalline nature, this being 
especially noticeable in the deepest shades. 

It is interesting to observe that if a portion be vigorously ground in a mortar 
so that it loses its crystalline nature, the colour will be found to have changed to 
an orange shade. 

This red is now gradually falling into disuse and is not to-day manufactured 
to anything like the same extent as it used to be owing to its replacement by 
substitutes. These latter consist chiefly of red synthetic dye-stuffs struck on orange 
lead and barytes. 

Manufacture.—The best shades of Persian red are obtained by boiling over 
a direct fire a strong solution of bichromate of potash and pulp white lead, with 
the addition of a small amount of caustic soda. 

The reaction takes place according to the following equations :— 


2PbCO,,Pb(OH),-+4K,CrO,—3PbCrO,,Pb(OH), +K2Cr0, +00). 


Example 1. Bichromate of potash ; : . » OO 
Pulp lead ; : : ; : 500 ,, 
60 per cent. causticsoda . : : las 


Properties of Lead Chromes.—The properties of the lead chromes naturally 
varies enormously according to their colour, but in general they may be regarded 
as pigments possessing remarkably good body and exceptional brightness of tone. 
They have an extremely soft texture, with the exception of Persian red, which 
is apt to be coarse on account of its crystalline nature. 

The lemon chromes are readily affected by alkalies, turning to orange or 
chrome red ; for this reason they cannot be used for distempers or lime colours. 

On exposure of hydrogen sulphide they darken owing to the formation of 
black sulphide of lead. 

The chromes are all completely soluble in a dilute solution of nitric acid, which 
affords a ready means of testing their purity, any adulteration such as barytes, 
gypsum, lead sulphate bottoms being left behind as an insoluble residue. 

When ignited the chromes turn dark brown with the evolution of oxygen and 
leave behind a residue of oxides of lead and chromium. 

The strength of a chrome is best determined by adding to it a definite amount 
of Chinese blue and comparing the green shade produced against the standard 
chrome similarly treated. By this means the cleanness of a chrome (also a blue 
if a standard chrome is taken) may be readily seen. 

Specification.—The general specification required of a chrome is as follows :— 

1. The chrome must contain 98 per cent. of lead compounds and be 
free from all added material such as lead sulphate bottoms, barytes, terra 
alba, and so on. 


YELLOW PIGMENTS 75 


2. It must be fine in texture, free from all coarse particles, and equal in shade 
to the approved standard. 

3. On reduction with ten times its weight of zinc oxide in linseed oil the 
resultant shade must be equal to the standard similarly reduced (strength test). 

4. It must contain less than 0-5 per cent. of moisture and not more than 
2 per cent. of water soluble matter. 

Method of Analysis——The general scheme used in the analysis of the lead 
chromes will be now briefly outlined. It must be, however, first mentioned that 
it is always advisable to conduct a quick preliminary qualitative analysis as much 
subsequent labour will in many cases be saved thereby. 

1. Movrsture.—Heat 5 gms. at 100° C. till constant. 

2. Insoluble.—Barytes (occasionally silica or China clay). Boil 1 gm. of pigment 
for half an hour with 50 c.c. concentrated hydrochloric acid, adding a little reducing 
agent, such as alcohol. Filter, wash thoroughly, ignite, and weigh. 

Note.—lf lead bottoms are present in the chrome, as they frequently are, pro- 
longed boiling is necessary to ensure that they are completely dissolved, inasmuch 
as this body is very much more insoluble than the sulphate of lead, which is directly 
precipitated along with the chrome. 

3. Lead.—The filtrate from the insoluble is evaporated to dryness to remove 
the excess of acid, then taken up with a few drops of hydrochloric acid and diluted 
with 250 c.c. of hot distilled water. Hydrogen sulphide is passed through till the 
solution is saturated and all the lead is precipitated. Filter, wash, and 
dissolve the precipitate in. dilute nitric acid. Precipitate and weigh as 
sulphate of lead. 

4. Chromium.—the filtrate from the lead sulphide is boiled to remove all 
hydrogen sulphide; then made alkaline with ammonia. The precipitate of 
chromium and aluminium is treated with a hot solution of sodium peroxide till 
dissolved ; it is then made up to 250 cc. 50 c.c. are filtered out, acidified with 
acetic acid, and excess of lead nitrate solution added. 

Filter off, wash, dry, and weigh as PbCrQ,. 

5. Aluminium.—Take 100 cc. of the 250 c.c. solution and acidify with 
hydrochloric acid. Re-precipitate with ammonia, wash and ignite, and 
weigh as Al,Og. 

6. Calcium.—To the filtrate from the iron and alumina add ammonia and 
ammonium oxalate. Ignite precipitate—calcium oxide (CaQ). 

7. Sulphates.—Dissolve 2 gms. of the chrome in hydrochloric acid, filter off 
insoluble and precipitate hot in dilute solution with barium chloride. Weigh as 
barium sulphate. 

Or the lead may first be removed by precipitation with aluminium and then 
the barium chloride added to precipitate the sulphate. 

8. Carbonates.—Estimate in the Schrétter apparatus in the usual way. 

The following analysis by the author of the various pure chromes will give the 
reader a clear idea as to their composition :— 


76 THE CHEMISTRY OF PAINTS 
Result of the Analyses of Pure Chromes 














Pure Primrose. Pure Lemon. 
Lead sulphate , . 26-70 per cent. Lead sulphate . 19-20 per cent. 
Lead chromate . . 68-35 i Lead chromate . 160 55 
Alumina : ; = DD bs Alumina : . 290 “3 
98-60 +, 03-60 fae. 
Pure Middle. Pure Orange. 
Lead sulphate : . trace Lead chromate . 19-90 per cent. 
Lead chromate . . 90-50 per cent. Lead carbonate . 18-70 3 
Lead carbonate . esa 9 se 
97-99 5 98-60 ” 
Pure Persian Red. 
Lead oxide . ; . 78-30 per cent. 
Chromic oxide , . 17-80 . 
96°10. 95, 
Analyses of Genuine Chromes 
Genuine Lemon Chrome. Genuine Orange Chrome. 
Lead sulphate : . 35-50 per cent. Lead chromate . 72-00 per cent. 
Lead chromate . . 64-00 # Lead carbonate . 7:25 ® 
Alumina, etc. : . 0°50 “ Red lead : . 20-50 a 
100-00 __,, 99-75 yy 
Analyses of Reduced Chromes 
No. 3 Lemon Chrome. No. 1 Middle Chrome. 
Lead sulphate . a8 (15bOper cent. Lead chromate . 45-50 per cent. 
Lead chromate . . 22°65 ‘3 Lead carbonate . 4°90 re 
Calcium sulphate . . 82:75 e Barytes .. . 49-42 3 
100-90 i, 99-82" 4, 
No. 3 Chinese Red 
Lead chromate. . 15-50 per cent. 
Red lead (Pb,0,) . . 50-20 3 
Barytes : . . 30°55 s 
96-25 RS 





This sample contained a dye-stuff soluble in alcohol. 


YELLOW PIGMENTS 77 


Zinc CHROME 


(Zinc Yellow, Zinkgelb, Jaune de Zinc.) 


Zinc chrome consists essentially of zinc chromate (ZnCrO,), but on analysis 
it is found that there is always associated with it a certain proportion of potassium 
bichromate and also zinc oxide. 

Manufacture—In the manufacture of zinc chrome it is essential that only 
the best grades of zinc oxide are used, such as the “Snow White” brands. The 
presence of any lead or iron in the zinc oxide is very objectionable in the prepara- 
tion of a first-class product. On the manufacturing scale the process used is as 
follows :— 

The zinc oxide is pulped up in water on flat stones so as to get it into a very 
fine state of sub-division ; it is then transferred to the precipitating vat and mixed 
up with cold water to a thin cream. The requisite amount of concentrated 
sulphuric acid (C.O.V.) is next cautiously added whilst stirring so as to convert 
a proportion of the zinc oxide into sulphate of zinc. 

After stirring for one hour a hot bichromate of potash solution. is next run in 
from the dissolving tubs. The precipitated zinc yellow thus formed is allowed to 
settle and the top liquor, which always contains excess of potassium bichromate in 
solution, is run off. 

As the zinc chrome is rather soluble only one wash is given before filter-pressing 
and drying. 

The best temperature of precipitation is about 120° F. If the temperature gets 
too high or too low a very coarse crystalline product is produced, which is useless 
as a pigment. 

The following example will illustrate the proportions which may be used to 
produce a good bright shade of zinc chrome. 


Example—dZinc oxide ; F ‘ : . 100 lbs. 
Potassium bichromate : 2 Sat ore. 
Sulphuric acid cone. . F ; Ces eee 
Yield ; ‘ : ’ PAY ES Nee 


Properties.—Zinc chrome is a yellow pigment having a bright clean pale shade. 
It is readily soluble in all mineral acids, also (unlike lead chrome) in warm dilute 
acetic acid. 

On heating it changes to a dark purple tint due to its decomposition to zinc 
oxide and chromium oxide. It is not affected by lime or sulphuretted hydrogen ; 
hence it is largely used for the production of lime yellows for tinting distempers. 
Zinc chrome is unfortunately lacking in body and strength as compared with 
chrome yellow. 

In conjunction with Chinese blue we get the useful non-poisonous range of 
zinc greens which are finding increasing favour in the paint trade. 


78 THE CHEMISTRY OF PAINTS 


Specification.—The general specification required for zinc chrome is as follows :— 

The zinc chrome must be of a soft texture and equal in colour to the standard 
shade. 

It must be free from any lead compounds or aniline dyes, or any added matter 
whatever such as zinc oxide, whiting, barytes, etc., and should be completely 
soluble in a hot dilute solution of acetic acid. On reducing with ten parts of zinc 
oxide in linseed oil the resultant shade must be equal to the standard sample 
reduced to a similar extent. 


An Analysis of a Pure Zinc Chrome 





Zine oxide : : : : : . 15-50 per cent. 
Zinc chromate . ; f ; : . 64-25 r 
Soluble matter (by difference) . ; .. AO 
100-00 si, 
Method of Analysis 


(A) Gravimetric. Dissolve $ gm. of the zinc chrome in dilute hydrochloric 
acid. Should there be any insoluble this must be filtered off, dried, and weighed= 
barytes or silica. Add 250 c.c. distilled water and about 2 gms. of ammonium 
chloride. Boil and precipitate with excess of ammonia. Filter and wash well. 
Ignite and weigh as Cr,O,. 

Zinc.—Add colourless ammonium sulphide to the filtrate from the chromium. 
Boil well to coagulate the precipitate (zinc sulphide). Filter and wash. 

Then dissolve the zinc sulphide thus obtained in dilute hydrochloric acid. Boil 
to remove all sulphuretted hydrogen, and precipitate with anhydrous soda 
carbonate. Filter and wash. 

Ignite the zinc carbonate precipitate to zinc oxide and weigh. 

Volumetric Estimation—The amount of zinc chromate may be volumetrically 
estimated as follows :— 

Weigh out $ gm. Add 50 cc. (or 100 c.c. if necessary) of ferrous sulphate 
solution (30 gms. FeSO, to 1 litre water). Titrate with standard bichrome solution 
(10 gms. to 1 litre water), using potassium ferricyanide as outside indicator. 


Example— 
50 c.c. FeSO,=26-1 c.c. K,Cr,0, solution. 
+ gm. ZnCrO, requires 100 c.c. FeSO, solution from pipette. 
2x50 c.c. FeSO, solution =52:-2 ¢.c. K2Cr,0, solution. 
Amount of K,Cr,0, required for excess FeSO,=26°5 c.c. 
52-2 ¢.c.—26-5 ¢.c.=25-7 c.c. K,Cr,0,. 
1 gm. K,Cr,0,=1-227 ZnCrO,. 
Loe. Ko0r,0;=-01 pm KCr05, 
Therefore ZnCrO,—64 per cent. 
Note.—This method is also applicable for the volumetric estimation of lead 
chromate. 1 gm. K,Cr,0,=2-196 gms. PhCrO,. 


YELLOW PIGMENTS 79 


We have now described the preparation and properties of the most important 
inorganic yellow pigments in general use. (For a description of the yellow lake 
colours see Chapter XIII. on Lakes). 

There are also a number of other yellow pigments which are known and have 
a limited use for particular purposes, but for a detailed description of these the 
reader is referred to the various reference books which deal exclusively with this 
subject. Mention, however, may be made of the following :— 

Barium Chrome or Barium Chromate (BaCrO,).—This is made by adding a 
solution of barium chloride to a solution of sodium bichromate. This pigment 
has a pale yellow colour, and lacks body. It is used to a small extent by paper 
stainers. 

Naples Yellow (Jaune de Naples).—Naples yellow is a compound of the oxides 
of antimony and lead, and always contains an excess of lead oxide. There are 
various shades of this yellow according to the particular method of its preparation. 
It is chiefly used in oil by artists. 

Cadmum Yellow (CdS).—This pigment is a sulphide of cadmium, and is mainly 
used by artists. The shades vary from yellow to orange. The following equation 
represents its method of formation :— 


CdS0,-+Na,S =CdS+Na,S0,. 


King’s Yellow (As,83) (Konigs Gelb).—This pigment is a sulphide of arsenic. 
It occurs in nature as the mineral orpiment. 

Realgar (Arsenic Orange) (As,S,) is a disulphide of arsenic and occurs native 
as tealgar. It has a pale orange-red colour, and has been used as a pigment by 
artists. 

Cassel Yellow is an oxychloride of lead of the composition PbCl,,7H,O, obtained 
by heating lead oxide and ammonium chloride. It is no longer used as a pigment. 

Aureolin (Cobalt Yellow).—This yellow pigment was discovered by Fischer. 
It is a compound of the nitrates of cobalt and potassium represented by the 
formula K,CO(NO,),. This pigment has a fine transparent yellow, but is only 
moderately permanent. 

It has been used to a limited extent as an artists’ colour. It is prepared by 
mixing an acid solution of a cobaltous salt with a concentrated solution of potassium 
nitrate. 

Indian Yellow (Purree, Puiri)—This interesting and curious yellow pigment 
is an organic body, but may be mentioned here briefly for the sake of convenience. 

It is an impure magnesium salt of euxanthic acid (C,,H,,0,,Mg, 5H,0), and 
is made at Monghyr, a town in Bengal, from the urine of cows which have been 
fed on mango leaves. 

The fresh urine, of a bright yellow colour, is boiled down in earthenware vessels, 
and the yellow deposit thus formed is collected on calico, made into balls, and sold 
in the bazaars. 

Pure Indian yellow has a deep transparent yellow colour of considerable beauty. 
It is used as a water and oil colour by artists, but is only moderately permanent. 


CHAPTER VIII 


THE BLUE PIGMENTS 


THE ultramarine blues and the Prussian blues are by far away the most important 
blue pigments, and those in most extensive use at the present time. The remaining 
known blue pigments, such as the various copper and cobalt blues that have been 
introduced from time to time, have all been gradually superseded by one or other 
of them, and at the present time they do not come on to the market in any quantity, 
and their use is now very limited. 


ULTRAMARINE BLUE 
(Ultra Blue) 


This pigment is by far the most important of the blue colours. 

Historical.—Ultramarine occurs in nature as lapis lazuli, a beautiful, blue- 
coloured crystalline mineral found in Siberia, Persia, Thibet, and China. Analysis 
shows it to be a silicate of aluminium and soda, with some combined sulphur. 

It was largely used by artists in the Middle Ages, who prepared it for use by 
repeatedly grinding the mineral in water to an extreme state of fineness and washing 
through fine strainers. 

Owing to the scarcity of the mineral lapis lazuli, and to the elaborate and tedious 
method of its preparation, genuine ultramarine was extremely costly. On this 
account endeavours were made to produce it artificially, and so successful have 
these been, that at the present time the whole of the ultramarine used in commerce 
is made artificially. 

Guimet of Toulouse, the eminent French manufacturing chemist, studied the 
production of ultramarine, stimulated by the offer of a prize of 6000 francs by the 
Société d’Encouragement de France in 1824 to anyone who should succeed in 
manufacturing ultramarine artificially at a cost not exceeding 300 francs per 
kilogramme. He was awarded the prize in 1828, being the first to devise a suitable 
process for its manufacture. 

Christian Gmelin of Tiibingen about the same time published a full description 
of his method of making it. 

Kottig also perfected a process for the production of artificial ultramarine at 
the Royal Porcelain Works at Meissen in about 1828, and this works was for many 
years one of the leading producers of this material. 

80 


BLUE PIGMENTS 81 


The great bulk of the material on the market at the present time comes from 
Germany and France. There are, however, a few works in England, Belgium, and 
the United States. 

The Manufacture of Ultramarine.—At the present time the manufacture of 
ultramarine is carried out, as a rule, by firms which are engaged exclusively in the 
production of this material; in other words, it is a special industry. The reason 
for this is that not only are the technical difficulties to be overcome very great, 
but a vast amount of experience is necessary in order to produce high-class grades ; 
in addition a special and very expensive plant is required. 

A brief account of the manufacture of this blue, according to the most modern 
methods, will now be given. The reader who wishes an exhaustive account is 
referred to those books dealing exclusively with the subject (see Bibliography). 

The artificial ultramarines that come into the market may be divided into three 
varieties as follows :— 

1. Sulphate Ultramarine, which is a pale greenish blue colour. It possesses 
little covering power, and is readily acted on by a solution of alum. 

2. Soda Ultramarine A (containing only a little sulphur), which is a dark blue 
colour. It has more covering power than the sulphate ultramarine, but is not so 
readily acted on by alum solutions. 

3. Soda Ultramarine B (containing a high percentage of sulphur), which is a very 
dark blue colour with a reddish tinge. It also contains a higher percentage of silica 
than the (A) variety, which makes it very resistant to alum solutions ; hence it is 
largely used in the paper trades. 

The raw materials used in the manufacture of ultramarine are :— 


(1) China clay (kaolin). 

(2) Soda ash. 

(3) Anhydrous sodium sulphate. 
(4) Sulphur. 

(5) Coal, charcoal, rosin, pitch, etc. 
(6) Kieselguhr, silica, quartz, etc. 


The manufacture of the ultramarine may be divided into the following 
operations :— 


(1) The mixing and grinding of the raw materials. 

(2) Calcining the finely-ground material. (This gives green ultramarine.) 
(3) Grinding the green ultramarine to an impalpable powder. 

(4) Blueing the green ultramarine by roasting. 

(5) Finishing ultramarine. 


1. Toe MrxInc AND GRINDING OF THE RAW MATERIALS 


For the production of ultramarine it is essential that the mixed raw materials 
should be ground to a very fine state of subdivision. This is done in powerful edge 
runners or in ball mills. 


82 THE CHEMISTRY OF PAINTS 


The mixings in general use for the manufacture of the above-mentioned three 
varieties are roughly as follows, though of course each manufacturer has his own 
particular proportions which he has found by experience gives him the best results, 
and which he carefully guards as a trade secret :— 


Raw Materials Mixture. Sulphate Ultramarine. Soda Ultramarine. 

A. B. 

China clay . : 100 100 100 
Anhydrous soda salphate , 150 ne as 

Soda ash : : : “a 150 150 

Coals” 7. : : ‘ ‘ 50 30 10 

Silica. : : : : i 5 20 

Sulphur . : : : * 25 75 125 


2. CALCINING THE FINELY-GROUND Raw MATERIAL. GREEN ULTRAMARINE 


The finely ground material is packed tightly into a large number of fire-clay 
crucibles, which are fitted with lids so as to exclude the air. The crucibles are put 
into a large muffle furnace in rows, and packed one on the other till the oven is full. 

The furnace is then bricked up and heated slowly to a white heat and main- 
tained at this temperature for about eight hours. The fires are then drawn and 
the oven slowly allowed to cool down. This takes about two days, and care must 
be taken that the cooling down is gradual, otherwise the final product will be spoiled. 

The furnaces are built in series, so that as one is cooling down the other can be 
charged. 


3. GRINDING THE GREEN ULTRAMARINE 


The contents of the crucible, when cold, are emptied out into large ball mills, 
and finely ground. 

Formerly it was customary to grind the green ultramarine under water, and 
wash out the soluble soda salts present, then dry and powder again. But this pro- 
cess, on account of its cost, has been superseded by the dry grinding process without 
any detriment to the finished product. 


4, “ BLuEIne ’”’ PRocEss 


The powdered green ultramarine is next converted into blue ultramarine by 
the addition of sulphur and heating in a furnace at a low temperature. 

There are many ways of carrying out this operation and each country has its 
own peculiar method. The simplest method consists in spreading the green ultra- 
marine on the floor of a kind of modified reverberatory furnace. The fire is lighted 
and when the temperature is high enough to ignite sulphur, a quantity of this 
material is thrown on and well stirred up. When this sulphur has burnt out more 
is added, and so on till the whole of the green ultramarine has been converted into 
the desired blue shade. The blue mass of crude ultramarine is then raked out. 


BLUE PIGMENTS 83 


5. FInisHiInc ULTRAMARINE 


The coarse blue particles from the furnaces contain a considerable amount of 
Glauber salts, and before this crude ultramarine can be used as a pigment it is 
necessary to remove these salts, and, at the same time, to grind the crude material 
to an extreme degree of fineness. 

The usual method now in use is to lixiviate the crude material with boiling 
water in order to remove all soluble salts which are present, and then to grind this 
washed ultramarine blue between flat stones till the colour is fully developed and 
the required degree of fineness obtained. The ground material is then levigated, 
and the pasty mass spread on long drying hearths heated by waste heat from the 
furnaces. 

The dried ultramarine comes from the hearths in the form of large cakes or 
lumps, and is emptied into a ball mill where it is re-ground to the required degree 
of fineness. It is then sifted through 80-120 inch. sieves and is ready for use. 


PROPERTIES AND Uses oF ULTRAMARINE 


Ultramarine on account of its beautiful blue colour and permanency has come 
to be very largely used in many industries at the present time. It is extensively 
employed in the paint industry both as an oil paint, tinter, and whitener; also in 
lime washes and distemper paints owing to its valuable property of being unaffected 
by lime or alkalies. 

It is also largely used for the “ blueing ” of whites or yellowish white materials 
such as barytes, white paints, paper pulp, starch, zinc oxide, sugar, etc., whereby 
the resulting whiteness of the colour appears to the eye to be very considerably 
enhanced. 

Ultramarine is unaffected by heat. Although unaffected by alkalies it is 
readily acted on by even dilute acids. A characteristic test of ultramarine consists 
in heating a portion with a dilute acid ; the colour is at once discharged, sulphuretted 
hydrogen is evolved, and silica and sulphur are thrown down. 

Ultramarine is rather a transparent colour and somewhat lacking in body. 
When grinding to a stiff paste in oil there is always an unpleasant sulphur odour 
noticeable, which is characteristic of this pigment, and is due to the heat of the 
grinding operation causing an action between the sulphur and the oil used. 

Hot alum solutions tend to destroy the colour of the sulphate ultramarines, 
and on this account paper-makers choose the soda ultramarine, variety B (which 
contains a large amount of silica and sulphur), because of its more resistant 
properties. 

The cobalt shade ultramarine blue obtained by the action of ammonium 
chloride on ultramarine is in moderate request owing to the beauty and cleanness 
of its shade. 

Besides ultramarine blue other varieties are also known, such as the violet, 
red, and yellow ultramarines; but as these are practically never met with in 
commerce it is unnecessary to describe them. 


84 THE CHEMISTRY OF PAINTS 


CONSTITUTION OF ULTRAMARINE 


Ultramarine is a compound of silica, containing alumina, soda, sulphur, and 
combined sulphuric acid. 

The constitution of ultramarine is exceedingly complex, and many chemists 
have at different periods undertaken investigations with a view to elucidating the 
problem of its composition without, however, much success; due mainly to the 
many varieties there are according to the methods and proportions used in 
manufacture. 

Hoffmann considered ultramarine to be a double silicate of alumina and 
soda, combined with bisulphide of sodium according to the following formula : 
2(Al,Na.8i,0,))Na Sq. 


ANALYSIS OF ULTRAMARINES 


Moisture.—Heat 5 gms. in water oven till constant. 

Insoluble (Silica).—Dissolve 1 gm. in 50 c.c. concentrated hydrochloric acid. 
Take to dryness and bake on the hot plate to render all the silica insoluble. 

Take up with 10 c.c. hydrochloric acid and 100 c.c. hot water. Filter, ignite, 
and weigh as silica (810,). 

Test with platinum wire to make sure that no barytes is present. This is 
unlikely, as the adulterants added are as a rule terra alba, Paris white, or 
silica. 

Alumina (Al,0;).—Take filtrate from silica, warm up, and add ammonia in 
excess. This precipitates the alumina. 

Filter, wash and ignite, and weigh as alumina. 

Sodium Oxide (Na,O).—The filtrate from the alumina is neutralised with 
sulphuric acid, evaporated to dryness and ignited till all ammoniacal fumes have 
been given off, cooled and weighed=sodium sulphate. To convert to sodium oxide 
multiply by 0-4366. 

Total Sulphur.—Fuse 1 gm. with a mixture of potassium nitrate and potassium 
chlorate for about one hour. Dissolve the fused mass in hot water with the addition 
of concentrated nitric acid. Filter off the insoluble silica and add barium chloride 
to filtrate. 

Filter, wash well, ignite and weigh=barium sulphate 


BaSO, x 0-1373=sulphur. 


From this weight deduct the weight of sulphur present as combined sulphuric acid 
to find the quantity of sulphur actually present as sulphide. 

Combined Sulphuric Acid.—Weigh 2 gms. ultramarine blue; treat with dilute 
hydrochloric acid, filter, precipitate with barium chloride ; again filter, wash, ignite, 
and weigh as barium sulphate BaSO,.BaSO, x 0-3422—sulphur trioxide (SO,). 


BLUE PIGMENTS 85 


ANALYSES OF ULTRAMARINE BLUES BY THE AUTHOR 


The results of the following analyses which are here given were made by the 
author on ultramarine blues that were being employed in the manufacture of paint 
and for tinting purposes. 


i! 2 3 
Moisture. ; : : : 0-25 31 “12 
Silica . : f : : 41-50 38-00 14-50 
Alumina. : : : : ‘ 26-00 25-40 9-60 
Sulphur. é ; : ; ; 11-55 o16 3°62 
Sulphur trioxide . ; : Z 2-50 3°25 1-20 
Sodium oxide. : ‘ ; : 18-20 23°26 9-40 
Calcium sulphate . : : : ; y . 61-56 











100-00 100-00 100-00 











Note.—No. 3 was an ultramarine reduced with terra alba, known in the trade 
as lime blue. 


LIME BLUE 


Lime blue denoted originally a copper hydroxide mixed with calcium sulphate, 
and was obtained by adding milk of lime to sulphate of copper solution. This is 
now quite obsolete, and the only lime blues that come on to the market at the 
present day are :— 


1. Ultramarine blues heavily reduced with terra alba (see analysis above), or 

2. Aniline pigment colours, which are made by striking or precipitating a blue 
synthetic dye-stuff such as methylene, or similar blue dye-stuffi, on to a suitable 
white base. 


Lume Blues are very extensively used for adding to lime washes and for distemper 
colours. 


PRUSSIAN BLUE 
(Chinese Blue, Paris Blue, Berlin Blue, etc.) 


Introduction.—Prussian blue is one of the most valuable and widely used blue 
pigments at the disposal of the paint manufacturer. 

Enormous quantities of this blue are used in the paint and printing ink trades 
on account of the beauty and brilliancy of its colour and shades. Moreover, in 
association with chrome yellow in varying proportions, we get a most extensive 
and variegated range of green pigments known as the Brunswick greens, which are 
extensively used at the present time. 

Prussian blue was accidentally discovered about the year 1704 by Diesbach, a 
Berlin lake maker, who communicated his discovery to a French pupil of his named 
De Pierre, and who later started making this pigment in a small way in Paris. Hence 
the name Paris blue. 


86 THE CHEMISTRY OF PAINTS 


Wilkinson in London next commenced manufacturing the pigment, and 
gradually more and more colour firms took up its production, till at the present time 
many thousands of tons are produced yearly. 

Composition.—Prussian blue is a compound of iron, carbon and nitrogen, the 
carbon and nitrogen being combined in a cyanide thus :-— 


Fe,C,,Ni3 or Fe,Cyj,. 


On careful analysis it is found that true Prussian blues always contain potassium 
as an essential part of their composition, the formula of which may be represented 
as KFe(FeCy,). 


Raw Material—tThe chief raw material for the manufacture .of Prussian blue 
is prussiate of potash or potassium ferrocyanide— + 


(K,FeCy,+3H,O; molecular weight, 422). 


This salt comes on to the market in the form of large yellow tabular crystals, 
which are soft to the touch. 

Potassium ferrocyanide or yellow prussiate of potash is manufactured by 
calcining caustic potash with charred nitrogenous substances such as scraps of horn, 
blood, hide, clippings, etc., in the presence of iron filings. The black fused mass, 
when the reaction is over, is lixiviated with boiling water and evaporated down ; 
it is then run into pans and allowed to crystallise out. 

At the present time a large amount of ferrocyanide is obtained from gas-works 
by-products. The spent gas lime resulting from the purification of the coal gas is 
treated with caustic lime, calctum ferrocyanide being formed. This is decomposed 
by potash and potassium chloride into potassium ferrocyanide. In many of the 
largest gas-works, however, these by-products are now worked up directly so as to 
produce Prussian blue, and very large amounts are turned out annually in this way. 

Prussian blue is obtained as a deep blue precipitate when a solution of a ferric 
salt is added to a solution of potassium ferrocyanide. This reaction may be expressed 
according to the following simple equation :— 


3K,FeCy,+2Fe,(SO,);=FeCy,3+6K,S0,. 
Potassium ferrocyanide+Ferric sulphate=Prussian blue+Potassium sulphate. 
At this stage it will be convenient to consider the methods and processes in 
general use at the present time for the production of Prussian blues on the com- 
mercial scale. 


THE MANUFACTURE OF PRUSSIAN BLUE 


The manufacture of this colour on the large scale is attended with very 
considerable difficulties. 

In the first place, very large vats are required, since it is necessary to work with 
dilute solutions in order to get the best qualities and shades. Moreover, this 
pigment, by reason of its extreme degree of fineness of precipitation and its bulkiness, 
takes a very long time to settle out. 

This makes the washing and filtering operations very tedious and protracted, 


BLUE PIGMENTS 87 


and it will be readily seen that a large plant is necessary if the manufacturer is to 
produce any considerable quantity of these blues. 

Prussian blue, as has already been pointed out, is produced by adding a 
solution of a ferric salt to a solution of prussiate of potash. As ferric salts are 
not readily available, it is cheaper and more usual for the manufacturer to use 
ferrous sulphate. This salt when added to prussiate of potash gives a whitish pre- 
cipitate of ferrous ferrocyanide, which on oxidisation is converted into Prussian blue. 


Raw MATERIALS 


Ferrous Sulphate (FeSO,+-7H,0 ; molecular weight, 278).—This salt, commonly 
known as green copperas, is a pale bluish-green crystalline substance, which can 
be readily made by adding scrap iron to dilute sulphuric acid, thus— 

Fe+H,S0,=FeSO,+H,. 

The colour maker, however, hardly ever makes his own green copperas in this 
way, as he can buy it exceedingly cheaply owing to its being a by-product in various 
industries, ¢.g. it is obtained from the waste iron liquors of galvanising plants in 
large quantities, and is often sold to the blue manufacturer in the form of large cakes 
or slabs known as “ slab ” copperas. 

Prussiate of Potash used to be made by the colour maker in the early days of 
the manufacture of Prussian blue, but nowadays this is never done as the saving 
is trifling, and a much purer and better product can be bought from those chemical 
works which make a speciality of this salt. 

As will be readily understood, there are many methods in use for the manu- 
facture of Prussian blue, and each manufacturer has his own particular process 
and methods of working. An attempt, however, will be made to give a brief 
description of the most important methods that are now in use for the preparation 
of this pigment. 

The processes in use may for convenience be divided into two parts :— 

(1) The formation of the white precipitate of ferrous ferrocyanide. 

(2) Oxidation of ferrous ferrocyanide to ferric ferrocyanide or Prussian blue. 

The variations in the different processes of manufacture mainly consist in the 
way in which the white precipitate of ferrous ferrocyanide is oxidised to Prussian 
blue. The manufacturer produces ferrocyanide blues of varying shades at will 
according to which process or processes of oxidation he makes use of, as described. 
in the examples given below :— 


Process 1.—Oxrpisinc AGENT: BiIcHROMATE OF PoTasH+SuLPHURIC ACID 
100 lbs. prussiate of potash are mixed in about 90 gals. of hot water in the 
dissolving vat (see Colour House Plant, Chapter VII.), and well stirred till all is 
dissolved. 
90 lbs. of green copperas are next dissolved in about 90 gals. of hot water 
in another dissolving tub, well stirred until all is taken up, then 10 lbs. of concen- 
trated sulphuric acid added to clear the solution (this converts any ferric iron into 


G 


88 THE CHEMISTRY OF PAINTS 


the ferrous state). The green copperas solution is then run down into the pre- 
cipitating vat through the strainers, so as to remove any insoluble matter. 

The stirrers in the lower or precipitating vat are set going, and the hot prussiate 
solution rapidly run in. A greenish-white precipitate of potassium ferrous ferro- 
cyanide (KFe,FeCy,) is immediately formed. 

This body is readily oxidised in the presence of air, as may be seen by the 
bluish shade that appears on the top of the vat. The oxidising agents are next 
immediately added, as it is most important in order to get clean bright blues 
that the oxidation should proceed very rapidly. 

Practice has proved that the best and most convenient oxidiser—and which 
is the one now in general use—is a mixture of bichromate of potash and sulphuric acid. 

On to the white precipitate obtained as above there is next poured in, with 
constant stirring, 48 lbs. of concentrated oil of vitriol, and then 16 lbs. of lump 
bichromate of potash is added. The white mass immediately turns blue owing to 
its oxidation to potassium ferric ferrocyanide or Prussian blue KFe,(Fe,Cy,,). 

The reactions that take place may be simply expressed by the following 
equations :— 

K,FeCy,+FeS0O,—Fe,Fe,Cy,+2K,S0,. 
Potassium ferrocyanide-+-Ferrous sulphate=Ferrous ferrocyanide 
+ Potassium sulphate. 
Fe,FeCy,+K,Cr,0,+7H,SO,=Fe,Cy,,+2FeSO, +2K HS80,+Cr,(80,)3+7H,0. 
Ferrous ferrocyanide+ Potassium bichromate-+Sulphuric acid=Prussian blue 
+Ferrous sulphate+ Potassium hydrogen sulphate-+Chromium sulphate-+ Water. 


The temperature at which the whole reaction is carried out should be as high 
as possible, and if the solutions fall below 90° C. steam should be passed through 
so as to raise the temperature to near the boiling-point again. 

The precipitate of Prussian blue thus obtained is in an extremely fine state of 
suspension, and must be left for about twenty-four hours to settle, for it settles 
very slowly. 

The mother liquor is removed in the usual way by knocking out the plug holes 
in the sides of the vat one by one as the precipitate settles down. 

The blue is then washed with cold water two or three times till quite free. A 
quick test to see if the blue is free is to take a drop of the waste liquor out and test 
with blue litmus. If neutral, then filter press, and dry out in the drying rooms 
at a moderate temperature. 


Process 2.—Oxipistinc AGENT: BLEACHING POWDER 


The proportions used and the method of preparing the whitish-green precipitate 
of potassium ferrous ferrocyanide are precisely the same as described under Process 1. 

At this stage the method of procedure is as follows :—The whitish-green 
precipitate is well washed three times w.th cold water to remove all soluble salts, 
and then 30 lbs. of concentrated hydrochloric acid is added. 

A solution of bleaching liquor is made up as follows :—50 lbs. fresh bleaching 





BLUE PIGMENTS 89 


powder are stirred into 25 gals. of water for four hours, and then left to settle 
overnight. 

The clear liquor is then run into the thick white precipitate of potassium ferrous 
ferrocyanide (to which has already been added the concentrated hydrochloric acid) 
with constant stirring. By this means we get the whole of the white precipitate 
oxidised into the blue potassium ferric ferrocyanide. 

The Prussian blue is then washed, filtered and dried. 

Bronze Blue.—The blue obtained by this method has a beautiful reddish-bronze 
appearance, and is often on this account sold under the name of Bronze blue. 


Process 3.—OxripisiInc AGENT: PoTasstum CHLORATE AND 
Hyprocutoric Acip 


The method is the same as described in Process 2, but in this case the washed 
potassium ferrous ferrocyanide (white precipitate) is treated as follows :— 

The washed precipitate is well stirred and steam passed through to raise the 
temperature to about 180° F. Then 25 Ibs. of concentrated hydrochloric acid are 
stirred in, and immediately afterwards a solution made up of 15 lbs. of potassium 
chlorate dissolved in 10 gals. of hot water run in. 

The contents of the vat are stirred for three-quarters of an hour, then allowed 
to settle. The blue is next washed, pressed and dried. 

Chinese Blue.—The blue made by this process is known as Chinese blue, a 
name which is given to the best qualities of Prussian blue. Although it has precisely 
the same composition as Prussian blue, its physical characteristics are different. 

For example, Prussian blue is a dark reddish blue, with a red undertone, 
whereas Chinese blue is a much paler blue, and is characterised by having a pale 
violet shade with a green undertone. 

Chinese blue is largely used by calico printers and dyers, and also in the 
manufacture of Brunswick greens and zinc greens. 

Properties and Uses of Prussian Blue.—Prussian blue (also known as Paris 
blue and Berlin blue) possesses a characteristic dark blue’colour, and is largely used 
in the paint and printing ink trades. It is a brittle substance and extremely hard 
to grind to a fine powder. Great care is required in grinding the material, as any 
overheating is apt to cause the blue to ignite. 

The varieties known as Chinese blue, Milori blue and Steel blue are identical 
in composition with Prussian blue, but are considerably paler in shade. 

Prussian blue by special methods of treatment can be produced possessing a 
very highly bronzed coppery lustre, which is much esteemed (see Process 2); such 
blues are known as Bronze blues. 

Prussian blue is rather a transparent colour, and hence is deficient in covering 
power. It is fairly permanent to air and light ; but when used for tinting pale shades 
in conjunction with chrome and zinc oxide or white lead the colour tends to fly. 
It is insoluble in water, but completely soluble in a 10 per cent. solution of oxalic acid. 

Prussian blue is not acted on by dilute acids, but in the presence of weak alkalies 
is immediately decomposed into a ferrocyanide of the alkali and oxide of iron. On 


90 THE CHEMISTRY OF PAINTS 


the addition of excess of acid the blue colour is restored. On account of this action 
of alkalies in discharging the blue colour it is impossible to use Prussian blue in 
distempers or lime colours. This test affords a ready means of distinguishing 
Prussian blue from other blues. 

On gentle ignition Prussian blue is decomposed, leaving a reddish-brown residue 
of ferric oxide, the cyanogen burning off to nitrogen and carbon dioxide. 

Analysis of Prussian Blues——The scheme for the analysis of Prussian blues is 
as follows :— 

Moisture.—Weigh out 5 gms. and heat in water oven till constant. 

Iron.—Ignite 1 gm. in a crucible gently till all the blue colour has disappeared, 
but not so high as to render the oxide of iron difficult of solution. 

Dissolve in concentrated hydrochloric acid with the aid of heat. Filter off any 
insoluble. If any insoluble is present it is an indication that the blue has been 
adulterated. Test insoluble for barytes, silica, etc. Make up filtrate to 250 c.c. 
Pipette out 50 c.c. and estimate the iron by titrating with standard bichrome (see 
under Estimation of Iron in Iron Oxide, Chapter X.) by the usual method. The 
amount of iron (Fe) thus obtained multiplied by 3-03 gives approximately the 
amount of Prussian blue present. 

Aluminium (Al,0;).—Pipette out another 50 c.c. and precipitate the iron and 
alumina with ammonia. Boil, filter, wash and ignite. Calculate the alumina by 
difference. 

Calcium.—If present precipitate with ammonium oxalate. 

Alkali Metals (Na and K).—To the filtrate from the iron and alumina add a 
few drops of hydrochloric acid, evaporate to dryness, and ignite to expel ammonia. 
Weigh ; dissolve residue in a very small quantity of water, and the potassium is 
precipitated, and weighed as the double potassium platinic chloride. Calculate to 
KCl. Deduct weight of potassium chloride so obtained from the weight of the 
mixed chlorides, and the proportion of sodium chloride is found. Calculate to 
metallic sodium and potassium. 

Cyanogen.—This may be estimated by the usual Kjeldahl method. 

Analyses of samples of commercially pure Chinese blues give the following 
results :— 








1 2 3 
Alkali metal : 7:76 Moisture. 5 3:54 : : 5-61 
Iron . , /eso0sbg Water comb » S181 : . 15-46 
Cyanogen . . 52-25 Cyanogen . ss wah ¥I 0 - STE 
wo Tron . is Pape o ‘ . 29-48 
99-70 Alumina . ; 0-52 : : 1-82 
oa as Alkali metal (K) . 4-50 (Na) . 7-60 
Alkaline sulphate fe : : 2-31 
100-00 100-00 








(1, Parry and Coste, * The Analyst,” vol. xxi. 2 and 3, By the Author.) 


BLUE PIGMENTS 91 


Soda Blues, or Gas blues, are rather dirty Prussian blues, which have been made 
by substituting the prussiate of soda or soda ferrocyanide in place of the potash 
salt. Clean greens cannot be made from them. 

Owing to the scarcity of potash salts during the war the use of soda blue came 
very much into vogue, but when the price of the potash salt approximates to that of 
the soda, it is very much more satisfactory and economical to use the former. 

Specification for Prussian Blues.—The usual specification for a pure Prussian 
blue is as follows :— 

1. The Prussian blue must consist of a ferrocyanide blue without the addition 
of any added matter whatever, such as alumina, zinc oxide, barytes, terra alba, 
and so on. 

2. It should contain at least 20 per cent. of nitrogen and 30 per cent. of iron, 
and on ignition should leave about 30 per cent. of residue, all of which is wholly 
soluble in hot concentrated hydrochloric acid. 

3. It should not contain more than 1 per cent. of matter insoluble in a 10 per 
cent. solution of oxalic acid. 

4. It should not contain more than 1 per cent. of moisture, or 2 per cent. of 
matter soluble in cold water. 

5. On reduction with zinc oxide in linseed oil in the proportion of 1 part of 
pigment to 50 parts of zinc oxide, the resultant shade should be equal to the 
standard blue similarly reduced. 

Note.—If the Prussian blue is required for admixture with chromes for the 
production of Brunswick greens, then a Prussian blue with as little bronze as 
possible should be specified. 

Brunswick Blue or Celestial Blue.—This blue is largely used in the paint trade 
per se, and for the production of Brunswick greens in association with the chromes. 

It is manufactured by adding the requisite amount of the finest white barytes 
to the finished pulp Chinese blue in the vat, then pressing and drying. The amount 
of barytes added to the blue varies from 50 per cent. to 90 per cent., according to 
the quality required. 

Brunswick blue has a beautiful pale blue shade, and is nice and soft in texture, 
and also easily powdered; on this account it has largely come into use. It is 
sometimes made in the dry way by adding the Chinese blue, a little at a time, to 
the barytes on the edge runners ; but in this case the result is not so good, and the 
shade is not so well developed as by the wet method. 

Terra alba is sometimes used in place of barytes, but this is unsatisfactory 
by reason of its woolly nature. 

Three samples of commercial Brunswick blues analysed by the author gave the 
following results :— 


I 2 3 
Moisture . : : ROA HT 1-20 0-50 
Prussian blue . P . 12-50 23-80 10-75 
Barytes . : , . 86-75 75-00 Terra alba 88-75 








100-00 100-00 100-00 








92 THE CHEMISTRY OF PAINTS 


Soluble Prussian Blue.—Prussian blue, although insoluble in water, is soluble 
in oxalic acid, and this property is made use of for producing a “ Soluble blue.” 
This is made by dissolving the ordinary pulp Prussian Blue in a strong solution of 
oxalic acid and salting the dissolved blue out. The precipitate is filtered off, and the 
excess of the salts removed by washing with cold water. 

Soluble blue can also be made by adding a solution of ferric chloride into an 
excess of potassium ferrocyanide solution. The composition of this pigment is 
represented by the formula K,Fe,(CN),.Fe,, a potassium-ferric-ferrocyanide. 

It is less stable than the other forms of blue. 

This blue was formerly used for making ink, but it has now been superseded by 
the aniline dyes. It is, of course, useless as a pigment in the paint trade on account 
of its solubility. 

Turnbull's Blue (Gmelin’s Blue)—This blue was formerly prepared by 
precipitating ferrous sulphate with potassium ferricyanide (K,FeCy,). It was 
supposed to have a different composition from that of Prussian blue, viz., 
Fe;Cy,., but has been proved to be identical with it.1 It no longer comes on 
to the market under this name, having been superseded by Prussian blue. 

Antwerp Blue—This blue is still occasionally met with in the trade. It has a 
very pale blue colour, and may be described as a sort of Prussian blue lake, the base 
of which is alumina. It may be prepared by running a solution of prussiate of 
potash into a solution containing equal parts of ferrous sulphate, alum and zine 
sulphate. It is chiefly used by artists. 

A brief outline of the preparation and properties of the few remaining blue 
pigments that possess interest and are still used to a small extent for particular 
purposes will now be given. 


COBALT BLUES 
These blues are known in two forms, viz. (1) Smalts, a silicate of Cobalt, and 
(2) Cobalt Blue or Cobalt Ultramarine, which is an oxide of Cobalt. 


(1) Smatts 
This pigment is essentially a cobalt glass. Its composition is roughly— 
Silica (810,) : : ; : . 60 
Alumina (Al,O3) . : : ; Spe 
Potash (K,O) : 3 : : me 
Cobaltous oxide . 5 : : » OG 


It is prepared by fusing the cobalt ore with silica and potash. The cobalt glass 
thus produced is ground to a coarse powder. The strewing smalt obtained in this 
way was formerly much used by sign painters. 

On further grinding under water to a very fine powder we get smalts produced 
which were formerly used by laundresses, in the pottery trades, and for giving a 


1 Prussian Blue and Turnbull’s Blue v. Erich Miller [with Hans Lauterbach], ‘‘ J. pr. Chem.,” 1922 
[ii], 104, 241-258. 


BLUE PIGMENTS 93 


blue tinge to writing paper; also as a pigment in oil. The manufacture of artificial 
ultramarine has, however, caused this pigment to become obsolete. 


(2) CoBaLtt BLUE 
(King’s Blue, Cobalt Ultramarine, etc.) 


This is an oxide of cobalt, and is one of the most permanent blue colours with 
which we are acquainted. 

La Grange 4 states that the old masters used this oxide mixed with oil in their 
paintings, which is the reason why the sky and drapery in some old pictures are so 
durable a blue. 

It is prepared by adding a solution of soda carbonate to a mixed solution of 
cobalt chloride, and alum, drying the precipitate, and igniting. It is then washed, 
dried and powdered. 

Cobalt blue has a beautiful greenish-blue tint and is absolutely permanent. It 
is not acted on by heat, or readily by acids or alkalies. It is chiefly used as a pigment 
by artists, and in pale enamel tints and stoving enamels where absolute permanency 
is required ; also to a certain extent in the pottery trades. 

It is a very costly pigment, and on this account is often adulterated with 
ultramarine blue. 

Copper Blues.—The various copper blues, such as Bremen blue, mountain blue, 
blue verditer, are mainly basic copper carbonates (CuCO,, Cu(OH),). At one time 
they were very largely used, but have now become practically obsolete because of 
their lack of body and liability to change under exposure to air and light. As their 
place has now been taken by ultramarine blue, it is necessary to enter into details 
regarding their manufacture. 


1 La Grange, “ Manual of Chemistry,” vol. i., p. 408. 


CHAPTER IX 


THE GREEN INORGANIC PIGMENTS 


THE inorganic green pigments may, for convenience, be divided into two 
groups, viz. :— 

(1) The naturally occurring green earth pigments and (2) the manufactured 
inorganic green pigments. 

The important group of green pigments derived from the aniline dye-stufis, such 
as naphthol greens, malachite greens, and others, will be discussed under the 
chapter on Lakes (see Chapter XIII.). 

By far and away the most important of the manufactured green pigments in 
general use are the group known as the chrome greens or Brunswick greens, which 
are manufactured in enormous quantities for use in the paint, printing ink, and 
linoleum trades. They consist of mixtures of chromate of lead associated with 
Prussian blue and barytes in varying proportions. 

The chief representative of the naturally occurring greens, and the only one 
which we will consider, is ““ Green Earth,” a natural occurring “ Augite,” which is 
fairly widely distributed in various parts of the earth’s surface. 


(1) THE GREEN EARTH COLOURS 
GREEN EARTH 
(Terra Verte, Griine Erde, Veronese Green.) 


Green earth occurs fairly widely distributed in various localities. It is found 
in Germany, France, Italy, Cyprus, and in Cornwall. 

The shade ranges from a dirty green to a pale greenish grey tint. Being a 
natural earth it is, of course, quite permanent, and from very early times has been 
employed as a pigment, the brightest and cleanest shades being selected for this 
purpose. Owing, however, to its lack of body and covering power it has been 
replaced as a pigment by the many manufactured green colours that have been put 
on to the market in recent years. 

Green earth is used in very large quantities in the colour industry on account 
of the peculiar property which it possesses of absorbing basic aniline dye-stuffs (see 
Lakes, Chapter XIII.), such as brilliant green, malachite green, auramine, methylene 
blue, and others, without the aid of any precipitating agent. 

The German green earths are the best absorbents, and are readily capable of 

94 


GREEN PIGMENTS 95 


fixing from 4 per cent. to 6 per cent. or more of these basic dye-stufis. Moreover, 
they fix them so firmly that they are remarkably permanent and are unaffected by 
lime, so that by means of this earth we are enabled to produce a large range of lime 
fast colours, which are of immense value in the distemper industry. 
Composition.—Green earth belongs to the very widely distributed group of 
earths or clays known as the augites, whose composition may be expressed thus :— 


[Mg(Fe)OCa0,S8i0, +(MgFe)O(AlFe),0.810,] ; 


that is, a magnesium ferrous silicated aluminium oxide. 
Analysis—Analyses of German green earths by the author gave the following 
tesults :— 


1 2 
Silica (Si0,). . 40-6 percent. Silica (Si0,) . , . 51-60 per cent. 
Tron oxide (Fe,0O,) 31:5 _,, Tron oxide (Fe,0;) . y NAGY 5, 
Alumina (Al,03) . Orne 55 Alumina (A1,03) : eee Lire 
Calcium sulphate . Oe Manganese dioxide (MnO,) trace 
Loss on ignition . 13-4 ,, Magnesia (MgO) ; ee OO ee 
——— Lime (CaO). : ey C Gai ber 
100-0 Sulphur trioxide (SO,;) . 2:74 ~~ ,, 
99-68 
3 
Moisture é ‘ 0-5 per cent. 
Loss on ignition . 7D ‘ 
Silica : ; 45-5 Ka 
Ferric oxide . : sO ais Tg 
Alumina : : 8-5 > 
Lime : , 1-5 e 
Magnesia sy. ee 
Potash ; : 7:5 rf 
99-1 


The green earths are prepared for use by a process of levigation, after which 
they are dried, ground and sieved. 

To test the suitability of an earth for use as a base for the basic aniline colours, 
take 100 gms. and add a solution of 3 gms. of the dye-stuff in hot water, stirring 
well. All the dye-stuff should be completely absorbed. When tested under the 
palette knife it should be of a smooth texture and free from all coarse particles. 
It should also be of a clean tone, otherwise the resultant lake would be dirty and 
lacking in brilliancy. 


96 THE CHEMISTRY OF PAINTS 


(2) THE MANUFACTURED GREEN PIGMENTS 
BRUNSWICK GREEN 
(Chrome Greens, Vert de Chrome, Chrom Griine, Milori Green, etc.) 


Originally the name Brunswick green was given to the basic chloride of copper, 
a pigment which is now quite obsolete. At the present time—as we have already 
mentioned—Brunswick greens are by far away the most important class of greens 
at the disposal of the paint manufacturer, not only on account of their brilliancy, 
high covering power and comparative permanency, but because of the wide range of 
shades which they provide, according to the proportions in which the constituents 
of the pigment are associated. 

Composition.—Brunswick greens are composed of a mixture of chrome yellow and 
Chinese blue, with varying amounts of barytes, according to the quality or grade 
of this pigment which the manufacturer desires to produce. 

Pure Brunswick greens—that is, mixtures of chrome yellow and Chinese blue 
only—are rarely called for. 


Manufacture of Brunswick Greens 


There are two methods in general use for the production of these greens, which 
will now be described in some detail. 

The Wet Method.—This method is the one generally adopted, because the green 
produced in this way is much brighter and more brilliant, and the admixture more 
perfect than by the “Dry Method.” Moreover, the tendency which these greens 
have to “ float,” 2.e. for the blue to come out on the top when made into paint, is 
thereby very considerably obviated. 

The method of procedure is as follows :— 

A chrome yellow is made according to one of the methods described under 
Lemon Chromes (see Chapter VII.), care being taken that the shade of the 
chrome is quite pale, or lemon yellow colour, and does not show any reddish or 
orange tinge in it. 

The chrome is well washed to remove any soluble salts; then the required 
amount of fine barytes is weighed out and added to this pulp chrome. The amount 
of barytes added varies, of course, according to the quality or grade of the Brunswick 
green that is being made. 

The barytes and chrome are then well stirred together till they are thoroughly 
mixed. Then a definite quantity of pulp Chinese blue is run in, with continuous 
stirring, until the desired shade is produced. 

The manufacturer knows from previous trials the weight of dry chrome that 
his batch of pulp chrome contains, and also the percentage of dry blue in the pulp 
blue that he runs in, hence he can gauge the amount of blue required to a nicety. 
To check this a sample of the finished green can be taken out and dried in the 
laboratory, and compared against the standard. 


GREEN PIGMENTS 97 


The green is then given a wash with cold water, pressed and dried; then 
runnered in the edge runners, and sieved through 80-mesh sieves. 

If the chrome has been made from lead acetate there is a tendency on 
drying out the green for it to turn dirty or “ foxy,” due to the formation of a basic 
or reddish chrome. This can be prevented by adding a little sugar of lead solution 
to the green just before pressing. In the case of lead nitrate chromes, which are 
more stable, this does not occur. 

The Dry Method.—This method simply consists in mixing the required propor- 
tions of Chinese blue, lemon chrome and barytes, and grinding under the edge 
runners till the shade is fully developed. This takes from one to two hours, 
according to the size of the batch. 

Another method consists in “ runnering ” or grinding the chrome with Brunswick 
blue to the required shade. 

The Brunswick greens that are made are known in the trade under the 
following designations :— 

(1) Pale Brunswick Green, (2) Middle Brunswick Green, (3) Deep Brunswick 
Green. Hxtra Pale and Extra Deep Brunswick Green are also made when specially 
required. 

The difference between the various shades of Brunswick green consist merely 
in the amount of Chinese blue they contain. 

Each of these shades of Brunswick green is made in five reduced qualities or 
grades, Nos. 1-5, No. 1 quality containing the least amount of barytes and No. 5 
the largest. 

Properties and Uses.—Brunswick greens are remarkable on account of their 
extraordinary good covering power and body. They possess beautifully bright 
and clean shades, and when made up into paint form work well under the brush. 

They are fairly permanent on exposure to light and air, and, in addition to being 
noted for their excellent anti-corrosive and protective properties, are highly decorative 
and pleasing to the eye. Hence they are very largely used for both internal and 
external painting. 

Very big quantities of Brunswick greens are also used in the linoleum trades at 
the present time. 

Brunswick greens when made up into paint that is used in outdoor work tend 
after some time to become darker or bluer, and, in fact, after two years’ exposure, 
in some cases it happens that the green colour has faded away and left nothing 
but the blue. This is due to the fact that the greens have not been properly prepared, 
traces of acid having been left in owing to faulty washing, and these acids have 
gradually dissolved out the chrome. 

For use in distempers or as lime colours Brunswick greens are unsuitable on 
account of the fact that alkalies turn the chrome portion orange or red, and at the 
same time destroy the Chinese blue. 

Exposure to acid fumes causes the greens to darken, and being composed of 
lead chromate they are naturally susceptible to sulphuretted hydrogen, which turns 
them black owing to the conversion of the lead chromate into lead sulphide. On 


98 THE CHEMISTRY OF PAINTS 


this account their use in gas-works or chemical works, where acid fumes are evolved, 
is precluded. 

Specification for Brunswick Greens.—The usual specification is as follows :— 

1. The Brunswick green shall be equal in colour and shade to the approved 
standard pattern. 

2. It shall consist of a lemon yellow chromate of lead and Chinese blue (ferro- 
cyanide blue) associated with barytes, and be free from any other added matter 
such as Paris white, terra alba, etc. 

Note.—The amount of barytes may be stated here. 

3. On reduction with ten times its weight of zinc oxide in linseed oil, the 
resultant shade shall be equal to the shade of the standard similarly reduced. 

4. The Brunswick green shall not contain more than 1 per cent. of moisture, 
nor 2 per cent. of matter soluble in water. 

5. The aqueous extract after shaking 10 gms. of the green with 50 c.c. of distilled 
water for one hour should be neutral to litmus. 


Scheme for the Analysis of Brunswick Greens 


(1) Movrsture.—Weigh out 2 gms. and dry at 105° for two hours. 

(2) Insoluble. 

Boil 1 gm. of the Brunswick green with concentrated hydrochloric acid, 
taking down to dryness twice to make sure that all the lead sulphate is dissolved. 

Filter off, wash well with boiling water, and dry on weighed filter paper= 
barytes-+Prussian blue. 

(3) Prussian Blue.—Gently ignite the insoluble residue to destroy the blue, 
and weigh. Estimate the iron present by potassium bichromate in the usual way, 
and calculate to Prussian blue by multiplying by 3-03. Barytes is got by difference. 

(4) Lead Chromate-—Now proceed according to the scheme for the analysis 
of lead chromate (see Chapter VII). 

Analyses of Brunswick G'reens.—The following analyses were made by the 
author on Brunswick greens which were being used in the manufacture of green 
paints in a large paint works, and will serve to give the reader a clear idea as to 
the composition of these pigments :— 


Brunswick Greens 


No. 1 Deep. No. 2 Middle. No. 3 Pale. 


Moisture : ; : . : 0-75 0-45 0:50 
Barytes . ; : ; ‘ ; 60-28 72°35 85:75 
Prussian blue . ‘ : : ; 8:27 4-25 1-79 
Chrome yellow : ; : : 24-45 17-27 7-31 
Lead sulphate : . : : 6-25 5-68 4-65 











100-00 100-00 100-00 


GREEN PIGMENTS | 99 


Emerald Tint Greens.—These greens are similar in composition to the Brunswick 
greens, but are, as their name denotes, of a chalky, bluish, green shade, 
approximating to the colour of genuine emerald green. 

Bronze Greens are dirty bronze shade greens, made from Brunswick greens, 
tinted with a considerable quantity of ochre and umber. 

Coach Greens are a deep bluish clean shade green, and are made from nitrate 
chromes treated with a little nitric acid. They are usually toned up with a small 
quantity of Dutch pink. 

There are many other Brunswick greens in common use of varying degrees of 
brightness and shade, such as the Royal greens, Albert greens, Moss greens, 
Hungarian greens, and so on; but as these can all be readily made from Brunswick 
green by the addition of tinters, a detailed description of them will not be necessary. 


Zinc GREEN 
(Vert de Zinc, Zinc Griin.) 


Zinc greens have come rapidly into favour during the last twenty years, not 
only on account of their bright clean shades, but also on account of their permanency, 
which is far greater than that of the Brunswick greens. 

These greens are composed of zinc chrome (zinc yellow), Chinese blue and 
barytes, and, unlike the Brunswick greens, are often sold in the pure state, 7. 
without the addition of any barytes whatever. They are manufactured, as in the 
case of the Brunswick greens, either according to the wet method or by mixing dry 
under the edge runner. 

Manufacture.—The best and cleanest shades are obtained, as with Brunswick 
greens, by adding the requisite amount of the pulp Chinese blue to the pulp zine 
chrome, prepared according to the method described under Zinc Chrome (see 
Chapter VII.). 

Large quantities are, however, made nowadays in the dry way by simply mixing 
the ingredients under the edge runner till the full shade of green is developed; this 
method gives excellent results, and at the same time, as will be readily understood, 
is much quicker and less costly than the alternative method. 

Properties and Uses.—Zine greens, equally with the Brunswick greens, can be 
made in a great variety of shades and qualities. The shades are clean and bright, 
of a fine smooth texture, and much more permanent than the greens made from 
the lead chromes; in addition these greens have the advantage of being non- 
poisonous. They are unaffected by sulphuretted hydrogen, and hence are largely 
used in oil as outdoor and indoor paints; they are also used for tinting enamels. 
Ground in oil they make very excellent protective and anti-corrosive paints, and 
retain their brilliant green colour in a remarkable manner. 

Zinc greens would be much more widely used but for the fact that they do not 
possess so great body and obscuring power as the Brunswick greens, and also that 
in comparison they are much more costly. 

This deficiency of obscuring power is due to the lack of body and strength of 


100 THE CHEMISTRY OF PAINTS 


zinc chrome component as compared with lead chrome. Zinc greens like Brunswick 
greens cannot be used as lime colours. 
They do not show the objectionable tendency to “ float ”—that is, for the blue 
to come to the top—which is so noticeable with the Brunswick greens. 
Analysis.—Two German zinc greens examined by the author had the following 
composition :— 











1. Pure Deep Zine Chrome. 2. No. 1 Pale Zine Green. 
Zinc chrome . ; : 72°80 Zine chrome ‘ : 36:80 
Chinese blue 5 ; 23-70 Chinese blue é q 10-41 
Zinc oxide : : , 3°50 Zine oxide . ; 5 12-14 
Barytes : : 40-65 
100-00 | 
100-00 





Scheme of Analysis.—For a scheme of analysis for zinc greens the reader is 
referred to the chapters on zinc yellow and Prussian blue, since by simple 
modifications of the schemes there given no difficulty will be found in making an 
analysis of zinc greens. 

Specification for Zinc Greens.—1. The zine green must consist of zinc chrome 
and Chinese blue (and barytes for reduced qualities), and be absolutely free from 
all lead compounds such as lead chrome, white lead, etc. 

2. It must be equal to the standard as regards shade and texture. 

3. On reducing with 1 part of green to 10 parts of zinc oxide in linseed oil the 
resultant shade must approximate the shade of the standard similarly reduced. 


CuRoMiIuM OXIDE GREEN 
(Green Oxide of Chromium, Guignet’s Green, Vert de Chrome, Griine’s Chromoxyd.) 


Green oxide of chromium (Cr,03) may be obtained by heating mercurous 
chromate in a retort till the whole of the mercury has distilled off. The residue 
chromium oxide possesses a beautiful bright greenish colour, and is one of the most 
permanent pigments that are known. 

It is unaffected by heat or light, and can be boiled with acids and alkalis without 
undgergoing change. 

There are many ways of producing this pigment, of which we may mention 
the following :— | 

1. Calcining a mixture of 3 parts of neutral potassium chromate with 2 parts 
of ammonium chloride. 

2. Calcining a mixture of potassium bichromate with either boric acid, 
sulphur or starch; by this means the chromic salt is converted into the chromium 
sesquioxide (Cr.0s). 

The usual process in use on the large scale for the production of this colour 
consists in the calcination of potassium dichromate with boric acid, and it is desirable 
to describe this method in some detail. 





GREEN PIGMENTS 101 


Manufacture of Green Oxide of Chromium.—Guignet was the first to publish an 
account of the preparation of this green; hence the name “ Guignet’s Green.” 
The green he prepared was the chromium tetrahydroxide of the formula Cr,0, ; 2H,0. 

In the form of a thick paste, and known as Guignet’s Green, this pigment is 
still largely used by calico printers. At the present time Guignet’s process is still, 
in all essentials, exactly as he described it; only in the furnaces where calcination 
takes place have there been any improvements. 

The method of working is as follows :— 

100 lbs. of potassium bichromate are ground up with 200 lbs. of boric acid so 
as to get an intimate mixture. The mixture is then put into a reverberatory furnace 
and heated for six hours to a dull red heat. 

The whole mass fuses ; a large amount of water is evolved, and a spongy mass 
of crude material is formed. After the reaction is complete the charge is raked 
out into vats containing cold water, and another charge is introduced into the furnace. 

The fused mass is well lixiviated to remove all the soluble salts (potassium 
borate and excess boric acid), then ground under flat stones, dried and re-ground.. 

As a large excess of boric acid must be used to produce a bright shade of green, 
it is customary to collect the first wash liquors and precipitate out the boric acid 
by the addition of an acid. 

The more dilute wash liquors are used to lixiviate the next batch of calcined 
crude material, and by this means raise the concentration of the solution so as to 
make the recovery of the boric acid worth while. 

The course of the reaction may be expressed by the following equations :— 


1. K,Cr,0,+16H,BO,;=Cr,(B,0,);-+K,B,0,+24H,0-+30. 
2. Cr,(B,0;)3+20H,0=Cr,0(OH),-+12H,BO,. 


Properties and Uses.—The shade of chrome-green varies slightly according 
to the particular process of its manufacture, but as a rule it is a deep greenish 
blue colour. 

Its covering power and strength are only moderately good. Its chief virtue 
lies in the fact that it is absolutely permanent, and for this reason is used in the 
engraving and the printing of bank notes. It can be mixed with any pigment 
without change, and has been used for producing a permanent green paint for 
stoving enamels. Acids, alkalies and heat have no action on it when properly 
prepared. Its more extended use is retarded on account of its comparative 
costliness. 

Scheme for the Analysis of Chrome Greens.—The analysis of these greens is 
rarely called for, as a qualitative test will readily indicate if it has been adulterated 
with any other green pigment. If required, all that is necessary is to take 1 gm. 
of the pigment and fuse with ten times its weight of fusion mixture, and precipitate 
the chromium after reduction with ammonia. As this green is only used to a 
limited extent, there is no need to give a specification for it, as the properties 
required have already been fully mentioned. 

The Copper Greens.—These greens were formerly very much used, but have 


102 THE CHEMISTRY OF PAINTS 


now been superseded by the more permanent Brunswick greens. The best known 
are (1) Emerald Green, (2) Verdigris, (3) Mineral Green, (4) Scheele’s Green, and 
(5) Green Verditer. 

We will now consider them briefly in the order of their importance :— 


EMERALD GREEN 
(Schweinfurth Green, Schweinfurtergriin, Paris Green, Imperial Green.) 


Emerald green was first made in 1814 at Schweinfurt from arsenic and verdigris. 

It is especially remarkable on account of the brilliancy of its colour, which is 
hardly equalled by any other known pigment. 

Composition.—An aceto-arsenite of copper, it may be represented by the 
following formula : Cu(C,H,0,).: 3Cu(AsO,)>. 

In 1822 Liebig, the great German chemist, made a thorough examination of 
this green and published the following process for its preparation :— 

Heat together equal parts of verdigris, acetic acid and white arsenic in twenty 
parts of water. Boil till the green develops, and add a little acetic acid from time 
to time to ensure that all the arsenite of copper is converted into the aceto-arsenite. 
Filter, wash and dry. 

The process in use at the present time for the manufacture of this pigment 
will now be described in some detail :— 


Manufacture. Raw Materials 


The raw materials used for the production of this beautiful green are sulphate 
of copper, white arsenic, soda acetate, or acetic acid, and soda carbonate. 

Care must be taken to see that the chemicals used are quite pure and free 
from iron; if this is not done serious injury may result to the shade of the finished 
product. For this reason it is essential, before starting operations, to test out 
thoroughly all the chemicals employed as follows :— 

Copper Sulphate-——The copper sulphate should first be tested by boiling up 
with dilute ammonia and filtering. Any reddish precipitate would indicate iron, 
and if present in more than minute traces the copper sulphate should be rejected 
as unsuitable. 

White Arsenic—1 gm. of the white arsenic should be sampled from bulk and 
ignited in a muffle in a fume chamber ; if it leaves more than 0-1 per cent. of residue 
it should be rejected as not being up to the required standard of purity. 

As a rule, in the case of acetic acid (or acetate of soda) and soda ash, the 
usual pure grades that are put on the market will be found satisfactory. 

The process as carried out on the large scale is as follows :—The soda car- 
bonate is dissolved in water in a copper steam-pan and half the required amount of ‘ 
the white arsenic carefully added. Steam is passed through till all the arsenic is 
dissolved ; then the rest of the arsenic is added and boiled till this is all taken up. 

This process takes about six hours’ hard boiling, and by this means (as is not 


GREEN PIGMENTS 103 


generally known) the soda carbonate is able to take up more than its theoretical 
amount of arsenic. 

The white arsenic dissolves, forming arsenite of soda, and carbon dioxide is 
evolved thus :— 

Na,CO,;+-As,0,=Na,As,0,+C0,. 
The resulting liquor of soda arsenite boils down to quite a syrupy consistency and 
must be diluted, and allowed to settle. 

The sulphate of copper is next dissolved in the precipitating vat in a fairly 
concentrated solution (1:25) by the aid of heat and constant stirring. When it 
has all dissolved and the temperature of the solution is about 90° C., then the top 
liquor of arsenite of soda in the copper pan is next run in rapidly at the boiling 
temperature, with continuous stirring, care being taken to pass all this liquor 
through a fine sieve in order to remove any solid undissolved particles that may 
be present. 

The requisite amount of a dilute solution of acetic acid (or its equivalent of 
a solution of acetate of soda) is next stirred in till the colour completely develops. 
Care must be used at this stage not to stir too much, as the beauty of the pigment 
depends on its somewhat crystalline nature, and the larger the particles the more 
brilliant is the resulting green. 

The emerald green is next washed well to remove all soluble salts, then filtered 
and dried at a low temperature, and finally passed through coarse sieves, after 
which it is ready for use. 

This pigment, on account of the arsenic which it contains, is exceedingly 
poisonous and dangerous to handle, and very special precautions must be taken 
during the whole process of operations to see that efficient ventilation is provided 
so that the workers do not inhale any of the dust. 

From a theoretical consideration of the proportions of the various in- 
gredients required for the production of this pigment, taken from the formula 
Cu(C,H,0,).; 3Cu(AsO,)., we obtain the following amounts :— 


Soda ash . : ; ; ; : ‘ Pots ibe: 
White arsenic . : : ; : : Oe 
Soda acetate . : : ; ; , at nae ee 
Sulphate ofcopper_. ; ; : J PLOOL r,s 


In practice, however, as already mentioned, it is found that only about half 
the above amount of soda ash is required. 
An excellent emerald green can be made working with the following 


proportions :— 
Soda ash . % : : : : ; . 100 Ibs: 
White arsenic . : : : : : a 2O0eF, 
Soda acetate . : ‘ 5 : ; PO ROUES 
Sulphate of copper. ; : : ; cars| eae 


Yield . : A : : : ay Ae 


104 THE CHEMISTRY OF PAINTS 


Care must be taken to regulate the temperature of the reacting solutions 
to a nicety, otherwise the shade of emerald green will vary enormously. It has 
been found by long experience that the best shades of emerald green are 
produced round about 90° C. 

Analyses of Emerald Greens.—The author has analysed many hundreds of 
samples of pure emerald greens at various times and they have all shown a 
remarkable uniformity of composition. The results obtained were as follows :— 


Highest. Lowest. 
CuO : 30-68 per cent. 30-20 per cent. 
As,O3° 3), (Oe OS, 55:50, 


The complete analysis of an emerald green is rarely called for, but the following 
will serve to show the average composition of this pigment :— 





Copper oxide . , ; ; : . 380-45 per cent. 

Arsenious oxide : , , : < BO-6D i 

Acetic anhydride ; ; j : . 13-90 - 
100-00 m 





Properties and Uses.—Emerald green possesses a beautiful bluish-green shade, 
quite characteristic of this pigment. It has fair body and covering power, and 
is moderately stable to light and air. It is wholly soluble in a solution of dilute 
ammonia, dissolving to a blue solution due to its copper content. It is also soluble 
in dilute acids. 

Formerly emerald green was largely used in wall paper colours and in the 
manufacture of paints of that colour, as also for linoleums, toy paints, etc. Of 
late years, however, owing to its poisonous nature, it has been completely given 
up for this purpose. Large quantities, however, are still manufactured annually 
for use as an insecticide, both for home and export. Canada, and before the war 
Russia, used to take a large amount of this pigment to use as a fungicide, for which 
purpose, on account of its poisonous nature, it is extremely valuable. A certain 
amount is also employed in the manufacture of anti-fouling paints (see Chapter III.) 
for use in painting ships’ bottoms to prevent the growth of weeds and barnacles. 


Scheme for the Analysis of Emerald Greens 


Copper.—Take 1 gm. of emerald green and dissolve in 20 c.c. hydrochloric 
acid; take down nearly to dryness, take up with about 30 c.c. water. Boil for 
several minutes. Wash into 8-oz. stoppered bottle. Bring slight precipitate 
down with caustic soda solution. Add a few drops of acetic acid in excess of dis- 
solving precipitate, then add 40 c.c. of 10 per cent. potassium iodide solution. Add 
at sodium thiosulphate solution from burette, drop by drop, taking care to add 
starch solution before end of reaction :— 


GREEN PIGMENTS 105 


1 c.c, = NanS0s solution=-0063 Cu. 


Cu to CuO xby 1°248. 


Arsenious Oxide.—Take 0-5 gms. of sample, distil in flask with hydrochloric 
acid (1H,O to 1HCl), catch distillate in an alkaline solution (NH,OH). Evaporate 
the contents of flask down three times with hydrochloric acid to make sure that 
all the arsenic comes over. 

Acidify distillate with hydrochloric acid, leaving only a few drops of acid in 


excess. Add soda bicarbonate in excess. Titrate with = iodine solution, using 


starch. 
Double number of c.cs. used and calculate, working on 1 gm. 


1G. of at iodine solution=-00495 As,Os. 


A quicker method for estimating the arsenic is as follows: Take 2 gms. of sample 
and dissolve up in 25 c.c. hydrochloric acid and 25 ¢.c. water. Keep solution at 
180° F. for five minutes, cool, and make up to 250 c.cs. in a measured flask. 

Draw off 25 c.c. of solution (=*2 gm. sample), place in No. 8 basin, dilute to 
about 300 ¢.c. bulk, and add solid soda bicarbonate, taking care to avoid spurting. 
Have large excess of soda bicarbonate. 

Titrate with freshly standardised iodine solution, using starch. 


Specification for Emerald Green 


(1) The emerald green must be a pure aceto-arsenite of copper, and be equal 
in shade to the standard sample. 

(2) On warming up with a dilute solution of ammonia, it must be completely 
soluble (0°5 per cent. of residue is permissible). 

(3) On reducing with zinc oxide and linseed oil in the proportion of 1 part of 
emerald green to 10 parts of zinc oxide, the resulting shade shall be equal to that of 
the standard treated in a similar manner. 


SCHEELE’S GREEN 


This pigment was discovered by Scheele, the celebrated Swedish chemist, in 
1778. It is an arsenite of copper with excess of copper hydrate, and has the formula 
CuAsO, ; Cu(OH),. 

It is prepared by dissolving arsenic in soda ash; then the hot solution of 
arsenite of soda is added to a hot solution of copper sulphate. The precipitate thus 
formed is washed with hot water and dried at a moderate temperature. 

Scheele’s green has a pale yellowish green colour, and possesses similar pro- 
perties to emerald green. As a pigment it is in every way inferior to emerald green, 
and on the discovery of the latter in 1814 its manufacture fell away till at the 
present time it is seldom or never met with. 


106 THE CHEMISTRY OF PAINTS 


VERDIGRIS 
(Basic Acetate of Copper, Vert de Gris, Griinspan.) 


Verdigris has been used as a pigment from very early times. It has been 
detected in the wall paintings of Pompeii, in many of the early Italian pictures, and 
its virtues offered a subject of discussion to medieval writers on the practice of 
painting. 

Verdigris is a basic acetate of copper, and may be represented by the formula 
Cu(C,H,0,)., 2Cu(OH),. This pigment is now no longer used by artists, its 
place having been taken by the more permanent greens derived from chromium 
and cobalt. 

Manufacture of Verdigris 


(1) French Process.—The chief source of supply used to be France, where in 
former times it was a sort of domestic industry. Almost every vineyard produced 
a certain amount of this green as a side line and an additional source of revenue. 

The methods in vogue are quite simple and crude, and consist in placing sheets 
or pieces of scrap copper in tubs along with the skins of grapes left after the juice 
has been pressed out. Acetic fermentation sets in, and after a few weeks’ time 
part of the copper has been converted into the acetate of copper or verdigris. 

When the grape skins are completely exhausted of acetic acid then the tubs 
are emptied out and the grape residue thrown away. The copper sheets, which are 
now covered with verdigris, are scraped clean, and are used over and over again 
with fresh supplies of grape skins till they are completely eaten away. The 
verdigris which has been scraped off the copper sheets is then collected in water, 
washed and dried. 

(2) Modern Chenucal Process.—The modern process for the production of this 
pigment is as follows :— 

Take 160 lbs. of copper sulphate and dissolve in hot water, making the solution 
very concentrated ; then run in a strong hot solution of acetate of soda. Boil for 
two hours till the verdigris starts to separate out. 

Cool; throw on to strainers and wash sparingly with cold water. The reaction 
may be expressed by the formula CuSO,+2CH,COONa=Cu(C,H,0,).+Na.80,. 

Properties and Uses.—Verdigris has a deep bluish green colour, and is of a 
coarse crystalline nature, hence it is rather hard in texture. It is slightly soluble 
in water, and very deficient as regards both body and covering power. 

Like emerald green, it is completely soluble in ammonia. Its composition is 
roughly as follows :— 


Copper oxide : ; ; . 43 per cent. 
Acetic anhydride . ; ‘ aed?) 2 
Water : ; : : Aart Be he, 


As a water colour it is of no use, as it rapidly fades ; in oil it is more permanent, 
but in time gradually goes black. | 
It is no longer used as a pigment, better greens having displaced it. Its chief 


GREEN PIGMENTS 107 


use at the present time is in anti-fouling compositions, its copper constituent rendering 
it destructive of all marine growths. A certain amount is used as verdigris paint 
in the tropics for the protection of wooden structures from the ravages of the 
white ant. 


MINERAL GREEN 
(Mountain Green, Malachite.) 


This is a natural basic copper carbonate having the formula CuCO,, Cu(OH),. 
The choicest specimens come from Siberia and Hungary. It is not now used as a 
pigment. The artificial mineral green that comes on to the market at the present 
time is of a different composition from the natural product, being as a rule simply 
a copper hydrate with a percentage of copper arsenite to brighten up the colour. 

It is made as follows: 100 lbs. of copper sulphate are dissolved in hot water, 
and to this solution are added 50 lbs. of caustic soda solution, in which 20 lbs. of 
arsenic have been previously dissolved. Stir well, wash, filter and dry at a very 
low temperature. 

This pigment is chiefly used as a poison in anti-fouling compositions, since 
as a pigment it is of little value, having all the usual defects of the copper greens. 

Green verditer is a basic copper carbonate, but is of no value nowadays as a 
pigment. 


CHAPTER X 


THE RED INORGANIC PIGMENTS 


Tue red oxides or iron reds have been used as pigments from time immemorial, 
and even now form by far the most numerous and important group of colours used 
by the paint industry. This is due not only to their decorative effect, but also 
because of their great permanency, covering power and durability, combined with 
their cheapness. 

These natural red oxides, or red earth colours, occur very widely distributed 
in different localities, and vary considerably both as regards purity and shade. 

Large quantities, as we will describe later on, are also manufactured from 
artificial sources, such as waste residues containing iron. 

Besides these red oxides of iron many other red colours are known which may 
be used as pigments, but those only will be described in detail which are at the 
present time of practical value and widely used as pigments, such as the red pigment 
obtained from lead and known as red lead, and the bright red from mercury known 
as vermilion. 

For description of Chrome Red, see Chapter VII. 


RED OXIDES OF IRON 


These oxides are obtained, as already stated, from naturally occurring earths 
and also by artificial means. 

(1) Manufacture from Natural Earths—Oxides of iron are widely distributed 
in nature, and vary considerably as regards shade and purity, 2.e. percentage of iron 
Fe,03. These deposits are found in various parts of England, America, Spain, 
France, Russia, India, and so on. 

One of the finest and brightest shades of the naturally occurring red oxides 
that are known comes from Ormuz in the Persian Gulf, and is shipped in large 
quantities to this country to be worked up as a pigment. It is sold under the name 
of Persian Gulf Red Oxide. 

Large deposits of very fine reds are mined in Spain and sold under the name of 
Spanish oxide ; as a rule they contain over 80 per cent. of iron oxide (Fe,0s). 

In France and England considerable quantities of red ochre from natural deposits 
are prepared for use as a cheap iron oxide pigment, and although low in iron content 
it has sufficient body and covering power to make it suitable for many purposes in 

108 


RED PIGMENTS 109 


the paint trade. It comes on to the market under such designations as Venetian 
Red, Vandyke Red, Red Ochre, etc. 

Native ferric oxide (Fe,03) occurs largely in various parts of England in the 
minerals hematite, specular iron ore, spathic iron ore, limonite, and so on. But 
these, as a rule, lack the necessary shade and tone to be of any use as pigments until 
they have been worked up. Considerable deposits occur, however, of a purple colour, 
selected seams of which give us the well-known ranges of light, middle and deep 
purple oxides. These latter are very rich in iron, and contain generally over 
90 per cent. of ferric oxide: they are largely employed for the manufacture of purple 
oxide and purple brown paints and colours. The process of converting the crude 
natural iron oxides into pigments is very simple, and usually all that is necessary 
is to grind it through special stone or steel mills to the required degree of fineness 
and then sieve. 

In some cases, where much stone and earthy material is mixed with the crude 
earth, a grinding and levigating process is necessary in order to produce a material 
of a suitable degree of fineness. 

(2) Manufacture from Artificial Products.—Large quantities of iron compounds 
which are by-products from various industries are worked up in different ways, 
so as to produce suitable coloured red oxides for use as pigments. 

Among such by-products may be mentioned green copperas (FeSO,; 7H,0) 
from galvanising works, waste iron residues from iron pyrites, which has been burnt 
to remove the sulphur content in the manufacture of sulphuric acid. 

The red oxides of iron thus obtained vary very greatly in shade from light red 
to deep purple brown, according to the temperature at which they are “ burnt ” or 
heated. They are sold under such names as Turkey Reds, Venetian Reds, Bright 
Red Oxide, and Indian Red. 


Process 1.—For the Manufacture of Turkey Red and Venetian Red 
TurKEY Rep OxIpDE 
(Colcothar, Caput Mortuum, Vitrioli, etc.) 


Turkey red oxide varies in shade from a yellowish red to a bright deep red ; 
it is one of the purest and strongest red oxides which are made. As a rule it contains 
from 93 to 95 per cent. of oxide of iron. 

The process of manufacture consists in heating waste copperas (a by-product 
as already mentioned), which is usually obtained in the form of large slabs from 
galvanising works, in a large reverberatory furnace at a bright red heat. 

The furnace is charged with the broken-up masses of copperas piled up about 
12 to 24 inches high on the bed of the furnace. The fires are lighted and the whole 
mass heated strongly for eight to ten hours. The furnace doors are occasionally 
opened to rake over the mass of red-hot material so as to obtain even distribution 
of the heat, and also to break up the larger masses of material that cake together. 

The furnace is connected by a long flue to a tall chimney in order to cause a 
strong draught to carry away the voluminous acid vapours produced. 


110 THE CHEMISTRY OF PAINTS 


When the iron oxide has reached the desired shade it is raked out hot and 
then well washed with water until all unburnt copperas is removed. It is then 
dried, crushed and sieved. 

The lower the temperature the paler are the shades of Turkey red produced, 
some being a yellowish red shade containing only about 85 per cent. iron oxide. 

Those produced at a higher temperature, and which are in most general demand, 
are of a rich bright red colour, and contain not less than 93 per cent. to 95 per cent. 
iron oxide. 

The course of the reaction may be illustrated by the following equations :— 

(1) 6¥eSO,.H,O=Fe,(SO,)3+2Fe,0;+380,+6H,0. 
(2) Fe,(SO,)3=Fe,03+380,. 

The escaping acid vapours are as a rule recovered and used to convert scrap 
iron into copperas for further burning. 

In the manufacture of Nordhausen or fuming sulphuric acid the copperas is 
heated in earthenware retorts, and the products of distillation (2.e. fuming sulphuric 
acid) are collected in earthenware receivers. 

The residue in the stills is known as caput mortuum, or colcothar, or jeweller’s 
rouge. By whichever process these oxides are obtained they require to be worked 
up for use as a pigment by grinding in water, levigating, drying and sieving. 


VENETIAN REDS 


Originally Venetian red consisted of a natural occurring ferric oxide or red 
hematite, but now the bulk of the Venetian red that comes on to the market is 
obtained by calcining green copperas, or other similar waste iron residues. 

The process of manufacture is similar to that described under Turkey reds. 
In this case, however, the copperas is mixed with whiting—more or less according 
to the quality of the Venetian red that is required. The mixture is then calcined on 
the bed of the furnace as mentioned above. The Venetian red thus produced does 
not require to be washed, but simply ground and sieved, and is then ready for use. 

2FeSO,(OH,)-+2CaCO,=Fe,0,+2CaSO,+2C0,+ H,0. 
The Venetian reds are very bright shade oxides, and contain as a rule from 12 per 
cent. to 25 per cent. of iron oxides, though occasionally in their purest state they 
may reach 50 per cent. iron oxide. 

Venetian reds are often made by simply grinding a very bright natural oxide 
or a Turkey red with terra alba to bring it down to the required shade and strength, 
and also at the same time to reduce its cost. 


InpIAN REDS 


These reds come on to the market in shades varying from light purple red to 
extra deep purple red. They contain generally over 90 per cent. iron oxide. 
Natural Indian red is a variety of pure red ochre or red hematite, and considerable 
quantities are imported from India. 


RED PIGMENTS 111 


These natural oxides are sometimes calcined to drive off the moisture, and so 
produce the required depth of shade. The bulk of the Indian red on the market is 
obtained by calcining copperas, or similar iron residues, in precisely the same way 
as described under Turkey Red. 

The deep purple shades of the artificial Indian reds are produced by adding 
salt to the copperas during calcination and increasing the heat very considerably 
over a much longer period. They are then washed, dried and sieved. 


Rep OXIDE 
(Red Ochre, Ruddle, Vandyke Red.) 


The common red oxides of iron that are in use as pigments are mostly natural 
oxides associated with variable proportions of mineral impurities, such as silica, 
alumina, and calcium carbonate. The iron content is round about 50 per cent., 
but, of course, varies according to the source of supply. Some of these native red 
oxides or yellow ochres are calcined at a moderate heat, so as to drive off the water 
of hydration and thus produce the required shade. Others simply require putting 
through the usual levigating process. 


Mapper Inp1an Reps, Tuscan Reps 


Red oxides are often brightened up with the addition of a permanent organic 
red such as alizarine lake, etc., and are then known as madder Indian, or Tuscan reds. 
These toners may be readily detected by boiling the red with an alcoholic solution 
of potash, when the dye-stuff is extracted. 

Properties and Uses of the Red Oxides.—The red oxides of iron are one of the 
most permanent, and at the same time the cheapest, pigments available for the 
manufacture of all red paints and protective coatings. They have excellent body 
and covering power, and may be employed in conjunction with all other pigments 
without undergoing change. They are not affected by air or light, and after pro- 
longed exposure show little or no sign of deterioration. Moreover, they possess 
very excellent protective and anti-corrosive properties, and are available in a large 
variety of shades, ranging from a pale yellowish red to the deepest purple. 

They are not readily acted on by either acid or alkali, nor by sulphur gases, 
and withstand a considerable amount of heat without change. 

For these reasons they are used in enormous quantities for painting all out- 
door wooden or iron structures, for colouring cement, rubber, linoleum, lime colours, 
and other colouring purposes too numerous to mention. 


Scheme for Analysis of Iron Oxides 


The following scheme for the complete analysis of iron oxides may be used ; 
as a rule, however, a determination of the iron content (Fe,Os) is all that is necessary. 
1. Moisture—Weigh out 2 gms. and heat in an air oven at 105° C. till constant 


in weight. 


112 THE CHEMISTRY OF PAINTS 


2. Combined Water.—Heat the above dried sample in a platinum crucible for 
two hours over a Bunsen burner to a dull red heat. Weigh till constant. 

If carbonates or inorganic matter are present, then this must be taken 
into consideration and allowed for, otherwise the result should be expressed as “ loss 
on ignition.” 

3. Insoluble Matter (Si0,, BaSO,)—Weigh out 1 gm. into a beaker, add 
50 c.c. of concentrated hydrochloric acid, and take down to dryness twice to render 
the silica quite insoluble. Take up with a few drops of hydrochloric acid and 150 c.c. 
of hot distilled water. 

Filter, wash well, and ignite ; equals insoluble matter. 

If barytes be present, and it is desired to separate the silica, then treat with 
hydrofluoric acid in a fume chamber. The insoluble residue should be quite white 
and show no reddish tinge, indicating that all the iron is dissolved out. 

In the case of very difficult soluble oxides, such as the natural purple oxides, 
it is often found that the last traces of iron are hard to remove. In this case a 
good plan is to add a few drops of stannous chloride solution to the hydrochloric 
acid, which reduces the iron and facilitates its solution. 

In the event of very refractory oxides it is sometimes necessary to fuse them 
with ten times their weight of fusion mixture (mixed carbonates of soda and potash) 
or else with potassium bisulphate before complete solution can be effected. 

4. Ferric Oxide (Fe,O3).—The filtrate from (3) is made up to 250 c.c., and 
50 c.c. are pipetted out into a white porcelain basin and brought up to the boil. 

Stannous chloride solution is run drop by drop till all the colour is discharged 
—that is, all the ferric iron is converted into the ferrous state—great care being 
taken not to add any excess of stannous chroride solution. 

100 c.c. of cold water are added, and when the whole solution is quite cold 
add 5 c.c. of mercuric chloride solution to remove any excess of stannous chloride. 
A very slight white milky precipitate is formed. If the solution turns black then 
the solution is too hot. If, on the other hand, a heavy milky precipitate is produced 
then too much stannous chloride has been used. In either of these cases it is 
better to throw the solution away and start afresh. 

Now titrate with standard bichromate of potash solution, using potassium 
ferricyanide as outside indicator. Check the result obtained by repeating the 
titration on another 50 c.c. of the solution. 

5. Alumina.—Take 50 c.c. and add ammonium chloride solution and ammonia. 
Boil, filter and wash well with hot distilled water. Ignite and weigh as alumina 
and ferric oxide, the alumina being obtained by difference. 

6. Calewwm.—To the filtrate from the iron and alumina add ammonia and 
ammonium oxalate solution. Boil well. Filter,wash and ignite; equals calcium oxide. 

7. Magnesium.—tTo filtrate from (6) add a solution of sodium hydrogen 
phosphate. Stir well and stand aside for six hours till all the magnesia has 
precipitated. Filter, wash and ignite. 

8. Carbonates (CO,).—Take 1 gm. and estimate CO, in the Schrotter apparatus. 
Calculate to CaCOs. 


RED PIGMENTS 1138 


9. Sulphate—Take 1 gm. and dissolve in hydrochloric acid. Remove iron 
and alumina as in (5), and precipitate the sulphates by the addition of barium 
chloride. Boil, filter and weigh as barium sulphate. Calculate to calcium sulphate. 

The following analyses by the author on various oxides of iron will give a 
clear idea as to the composition of these pigments :— 


1 2 3 4. 5 6 ie 
Moisture : é ‘ 0-0 030 0:46 0-75 0:35 0-25 , 0-45 
Loss on ignition . ; 142 2:25 135 3:25 . 794 1:15 2:38 
Silica Si0, tj. : 5 4:00 4-93 23-20 20-15 0-25 np 3°41 
Tron oxide Fe,O,_ .. i 90:05 85-25 64:00 55-50 82-54 95-32 90-00 
Alumina Al,O,  . 2:85 453 7-65 15-45 3-25 3-28 2-41 
Calcium CaO . : : del yee 22D Lente SOR eae) 1-35 
Magnesia MgO , ; Ose 0-28 gle 1-62) bbl. Se 








100-00 100-00 100-00 100-00 100-00 100-00 100-00 





8 9 10 1B) 
Moisture A : ; 0-20 0:35 0-45 0-63 
Loss on ignition . se, 1-50) (2:50.* 214 
Silica ; ; : 58 200 3:25 1:85 
Iron cxide . ; ; 99-80 96-15 13-00 50-00 
Alumina : < : i a 2:15° 4-25 
Calcium sulphate. : es ae 78-65 41-13 














100-00 100-00 100-00 100-00 














1. Purple Oxide. 2. Spanish Oxide. 3. Persian Gulf Oxide. 4. English Red 
Oxide. 5. Turkey Red Oxide (yellowish red shade). 6. Turkey Red Oxide (bright 
red shade). 7. Black Oxide. 8. Super Deep Indian Red. 9. Super Light Indian 
red. 10. Common Venetian Red. 11. Best Venetian Red. 


Specification for Red Oxide of Iron 


The red oxide of iron must be a finely levigated pigment and contain not 
less than 80 per cent. of oxide of iron (Fe,0,). 

It must be free from dye and any added materials such as barytes, Paris white, 
terra alba, silica, etc., and be equal in shade and texture to that of the standard 
sample. 

On reducing the oxide with ten times its weight of zinc oxide in linseed oil, 
the shade thus produced must be approximately equal to that of the standard 
sample. 

It must not contain more than 0-5 per cent. of moisture or more than 2 per cent. 
of matter soluble in water. 

Note.—In the case of Venetian reds the amounts of ferric oxide content may 


114 THE CHEMISTRY OF PAINTS 


be specified as low as 12 per cent. Fe,O3, whilst in the case of Turkey reds and 
Indian reds the percentage of Fe,O, required will be not less than 90 per cent. 


Rep LEAD 


(Minium, Mennige, Rosso Saturno.) 


This valuable red pigment, under the name of minium, was well known to the 
ancient Egyptians. It is a lead tetroxide and may be represented by the formula 
Pb,O,. In all probability it is a salt of plumbic acid, viz., lead orthoplumbate :— 


/O /O 
PbsPbO,orPbO ) Pb ope 
Red lead is produced by heating litharge (PbO) in the air at a temperature of 
about 480° C. It is not, as was once supposed, a mixture of lead monoxide and 
lead peroxide (2PbO+PbO,), for it has been shown that the dissociation pressure 
of lead peroxide at a given temperature is much less than that of red lead. 
Commercial red leads always contain Pb,O, with variable amounts of PbO; 
this amount of free litharge averages between 6 and 12 per cent. 
Manufacture of Red Lead.—In the manufacture of red lead the starting-point 
is metallic lead, and the process may be divided into two stages :— 
(1) The conversion of metallic lead into massicot (lead monoxide). This is 
known as “ drossing.” 
(2) The transformation of this product into red lead (Pb,0,; nPbO). 
The formation of red lead from metallic lead may be expressed by the following 
simple equations :— 
(1) 2Pb+0,=2Pb0. 
(2) 3PhO+O=Pb,0,. 


The conversion of the metallic lead into the yellow lead monoxide or massicot 
is carried out on the manufacturing scale as follows :— 


(1) Formation of Massicot or “* Dross ” 


The pig lead is thrown on the bed of a reverberatory furnace and raised to a 
dull red heat. The molten lead thus obtained is stirred from time to time with 
long iron rakes so as to expose fresh surfaces of lead to the oxidising influence of 
the air, and as fast as the yellow scum forms on the surface of the lead it is raked 
to the back of the furnace. 

Care must be taken not to raise the temperature too high, otherwise the scum 
or “dross” will be converted into the red litharge, which cannot be turned into 
red lead. 

The operation of converting the metallic lead into “dross” takes from 
12-24 hours, according to the size of the charge. 

The yellowish coloured massicot is then raked out and ground under water 


RED PIGMENTS 115 


and levigated. By this means the unchanged lead is removed, and the fine 
yellowish lead monoxide is dried ready for the next operation. 


(2) Conversion of Massicot into Red Lead 


The yellow massicot is next introduced into the same furnace again and 
heated at a low red heat in the presence of a large amount of air to ensure perfect 
oxidation. 

Care must be taken at this stage not to allow the temperature to get too high, 
otherwise the red lead would be decomposed according to the following reversible 
equation :— 

2Pb,0, == 6PbO+0,. 


The operation takes about 12-15 hours; towards the end of it samples are 
taken out from time to time and examined to see if the colour is up to standard. 
When this point is reached the contents of the furnace are immediately raked out. 

The red lead is then finely ground and is ready for use as a pigment. 

The manufacture of red lead, according to the above process, was originally 
only carried on in this country, and has attained a very considerable magnitude. 

Of recent years, however, the Germans have adopted our processes, and now 
large quantities of this material are made in Germany. Big quantities are also 
made at the present time in the United States by the nitrate and the basic oxide 
processes (see below). 

Red Lead from Lead Sulphate——Another process for the manufacture of red 
lead—which, however, has not been carried on to any extent—consists in calcining 
a mixture of lead sulphate, soda carbonate, and soda nitrate together in a furnace. 
The reaction proceeds as follows :— 


PbSO,-+Na,CO;=PbCO,-+Na,S0,. 
6PbCO,+2NaNO,=2Pb,0,+6C0, +2NaNO,. 


The fused mass is lixiviated with water, ground and dried. 

Red Lead by the Nitrate Process.—In this process metallic lead and nitrate of 
soda are fused together, yielding an oxide of lead and nitrite of soda thus— 
Pb+NaNO,=PbO+NaNO,. This oxide is washed to remove the nitrite of soda 
and calcined as above. The nitrite of soda thus recovered is used in the preparation 
of Para reds (see Lakes, Chapter XIII.). 

The Basic Oxide Process.—In this process, recently worked out in the United 
States, molten lead is atomised, 7.e. very finely divided by means of superheated 
steam. Thisis converted into a basic oxide by agitation with air and moisture, dried, 
ground, and calcined for twelve hours. This process gives an excellent fiery red lead. 

Properties and Uses of Red Lead.—Red lead possesses a bright scarlet red colour, 
and is very fine in texture. It has excellent body and is quite permanent, and 
has great density and hiding power. Its specific gravity is 8-6. 

When heated gently in air the colour changes to a dark brownish red, but 
regains its colour on cooling. 


116 THE CHEMISTRY OF PAINTS 


When strongly heated it decomposes, giving off oxygen. 

Red lead is completely dissolved by nitric acid in the presence of a reducing 
agent such as sugar or alcohol. This test furnishes a ready means of detecting 
the presence of any insoluble adulterants such as barytes, silica, and so on, which 
are left behind in the form of a white residue. 

This reaction may be expressed by the following equations :— 


2Pb,0,+4HNO,=2Pb(NO,),+PbO0,+2H,0. 
PbO, +2HNO,+C,H;,OH=Pb(NO;).+CH,COOH +2H,0. 

When heated with hydrochloric acid, lead chloride is formed and chlorine given 
off; with sulphuric acid lead sulphate is produced with evolution of oxygen. 

Red lead is largely used—made up into paint with linseed oil—as a priming 
or first coat for iron structures exposed to severe weather conditions. In fact, 
practically all first-class priming paints for iron and steel structures may be said 
to consist of red lead, or to contain a proportion of red lead as one of their 
constituents. 

Besides possessing excellent anti-corrosive properties, red lead exerts also a 
very powerful drying action on oils, so that paints containing this material dry 
rapidly, and with a hard film or surface. 

On account of this rapid drying or oxidising action of red lead on linseed oil 
it is customary to mix the red lead with the linseed oil just before using, otherwise 
the paint eventually sets up hard in the packages, rendering it unfit for use. 

The hardening or “ livering” of red lead ground in linseed oil is due to the 
litharge content. 

Recently a non-setting brand of red lead has been put on the market to obviate 
this difficulty. 

Red lead always appears to contain a certain amount of free litharge—some- 
times as much as 25 per cent.—which may be removed by treatment with lead 
acetate solution. 

On account of its hard-setting properties in linseed oil red lead is largely used 
in the making of hard-setting cements, lutes and packing for joints. 

Red Lead Substitutes or Imitation Red Lead.—These are simply red dye-stuffs 
struck on barytes, with sometimes a proportion of red lead added. 

Specification for Red Lead.—The red lead must be of a good bright colour, fine 
in texture, and equal in all respects to the standard. 

It must be genuine and contain no added matter such as litharge, barytes, dye, 
whiting, etc. It must contain not less than 90 per cent. true red lead content. 

It must contain not more than 0-5 per cent. of matter soluble in water. 


ORANGE LEAD 
(Orange Mineral, Orange Mennige.) 


This product has the same composition as red lead, but contains less free litharge. 
It is prepared by calcining white lead, or more usually white lead residues or 
tailings, in a furnace similar to that used in the manufacture of red lead. The white 


RED PIGMENTS Lie 


lead is heated at a low red heat for about twenty-four hours till the desired shade is 
produced. 

The decomposition of the white lead proceeds according to the following 
equation :— 

2PbCO;, Pb(OH),-+O=Pb,0,+2C0,+H,0. 

Properties and Uses of Orange Lead.—This pigment has a beautiful, bright, 
clean orange-red shade, and is exceedingly fine in texture. It is not so dense as 
red lead, having a specific gravity of 6-0. 

The litharge content of orange lead is usually very low, and for this reason— 
unlike red lead—it may be ground into linseed oil or varnish without any fear of its 
“ livering ” or “‘ feeding,” that is, setting up hard in the packages. 

Orange lead is largely employed as a base for aniline colours—e.g. cosine on 
orange lead—on account of its excellent body. 

It is very permanent and has excellent anti-corrosive and protective properties. 


Scheme for the Analysis of Red Lead and Orange Lead 


1. Mowsture-—Take 2 gms. and heat at 105° C. Weigh till constant. 

2. Insoluble.—Dissolve 1 gm. in semi-concentrated nitric acid, adding a little 
sugar, alcohol or other reducing agent. Dilute with boiling water. Filter if neces- 
sary, and wash well. Any insoluble denotes adulteration, and, if present, test 
for barytes. 

3. Total Lead.—Evaporate filtrate to dryness ; take up with as little hot water 
as possible. 

Cool, precipitate with sufficient sulphuric acid; add a little alcohol, and allow 
to stand for one hour. 

Filter through a weighed Gooch crucible, washing well with 50 per cent. alcohol. 
Dry and weigh as lead sulphate. 

4, Free Litharge—Weigh 5 gms. of the red lead and digest with a neutral 
solution of acetate of lead. 

Filtrate through a Gooch crucible, wash well with boiling water, dry and weigh. 

The weight of the residue subtracted from 5 gives the free litharge present. 

5. Dye-stuff—Boil up with alcoholic potash solution and filter. Any dye 
present will be at once apparent in the filtrate. This need not be estimated. 


VERMILION 
(Cinnabar, Zinnober, Vermilion.) 


The mineral cinnabar or vermilion has been used as a pigment from the earliest 
days, and mention of it has been found as early as 600 B.c. It was used by the 
ancient Hebrews for painting the walls of their temples. 

Pliny’s “‘ cinnabar ” or “‘ minium ” was true vermilion, though it has often been 
confused with minium or red lead. It is a compound of mercury and sulphur 
(mercuric sulphide), HgS, and occurs naturally as the mineral cinnabar in Spain 


(Almaden), Austria (Idria), China, Japan, Mexico, Peru, and numerous other places. 


118 THE CHEMISTRY OF PAINTS 


The native cinnabar was converted into a pigment by carefully grinding selected 
pieces and sieving. 

Although the ancients used the naturally occurring product, this has now been 
replaced by the manufactured article. 

The Chinese have been renowned as makers of vermilion for many hundreds of 
years, and even at the present time the variety produced in that country is the 
most highly esteemed. The process of manufacture used by the Chinese has always 
been very jealously guarded, and kept in certain families, where it has been handed 
down from father to son. 


MANUFACTURE 


The methods in use for the manufacture of artificial vermilion may be divided 
into two classes, viz. :— 

1. The Dry Method, in which the raw materials, mercury and sulphur, are 
combined in the dry state. 

2. The Wet Method, in which the reaction is carried on in solution. 


(1) The Dry Process 


The dry method for the production of vermilion is the older method of the 
two, and is the one used by the Chinese, even at the present time. The Chinese 
method, with modifications, was introduced into Europe by the Dutch, who, however, 
were not particularly successful with their process. Later the manufacture was 
carried on in Austria by an improved method. 

The original Dutch process was briefly as follows :— 

20 lbs. of sulphur are melted up in an iron pan, and 100 lbs. of mercury gradually 
added with continual stirring. The action is a very vigorous one, great heat being 
evolved, and it must therefore be carefully regulated as so to avoid explosions. 

When the reaction is complete, the fused black mass of black sulphides of 
mercury or “‘ethiops”’ is emptied out ready for the sublimation process. This 
latter is carried out in earthenware pots, or else in vertical iron cylinders fitted 
with heads and receivers. The pots or cylinders are placed in a furnace and so 
arranged that only the lower portion is heated. The “ ethiops”’ or black mercury 
sulphide is charged into the pots or cylinders, which are then strongly heated, 
whereby most of the excess of sulphur is burnt off; and as the heat increases the 
vermilion sublimes on the upper and cooler portions of the vessels. 

The pots are continually recharged, and when sufficient masses of sublimed 
red vermilion have accumulated, the pots are allowed to cool down and the vermilion 
is scraped off. 

The vermilion is then ground and well washed with a fairly strong solution of 
alkali so as to remove the free sulphur and black sulphide of mercury that are present. 
Finally, it is well washed with cold water to remove all soluble matter, and dried at 
a low temperature. 

Another method, which is an improvement on the Dutch process and gives a 
better yield, consists in mixing the sulphur and mercury in revolving drums for about 


RED PIGMENTS 119 


eight hours, whereby an intimate mixture of the materials takes place. The mixture 
of mercury and sulphur is then transferred to the sublimation pots, and treated as 
described under the “‘ Dutch process.”’ 


(2) The Wet Process 

This process is the one that has been adopted by the English and German 
manufacturers of vermilion. 

The original wet process was carried out as follows :— 

300 parts of quicksilver are thoroughly ground with 68 lbs. of sulphur ; towards 
the end of the grinding operation a little caustic potash is added to complete the 
transformation of the mercury and sulphur into the black mercury sulphide. The 
black mercury sulphide is then warmed up with a strong solution of caustic potash 
and constantly stirred. After some time the black mass gradually turns brown, 
and then scarlet red. 

Great care must be taken not to allow the temperature to exceed 50° C., other- 
wise the brilliancy of the colour will be impaired. Directly the red vermilion of the 
desired shade is produced cold water is run in and the vermilion well washed 
and dried. 

An improvement on this process consists in shaking mercury with potassium 
pentasulphide at a temperature of about 45° for two or three days. The liquor is 
then run off and the residue treated with a concentrated solution of caustic potash 
till the bright red shade of the vermilion is fully developed. The reaction that 
takes place may be expressed by the following equation :— 

Hg+K,8;=HgS+K,8,. 
This process gives an excellent yield, and the vermilion produced by it is equal in 
brilliancy to that of the vermilion obtained by the dry method. Moreover, it is 
very economical, as the mother liquor of potassium tetrasulphide only requires to 
be digested with flowers of sulphur to be reconverted into potassium pentasulphide, 
which may then be used over again. 

Properties and Uses of Vermilion.—Vermilion is a bluish-scarlet red powder, 
and comes on to the market as pale vermilion or deep vermilion. The pale vermilion 
is obtained from the more crystalline deep vermilion by repeatedly grinding it till 
the required shade is produced. It has a specific gravity of 8-2. 

It has very good body and covering power, and on account of its brilliant red 
colour was formerly very largely used, ground in oil and varnish, as a signal red 
paint. A little is still used by railway companies for this purpose, and also by coach- 
painters, who employ it as a lining colour. Owing to its costliness, however, and its 
tendency to turn black after long exposure, it has now been replaced by the cheaper 
permanent aniline (Alizarine, Fast Scarlet R) lakes. It is insoluble in alkalies and 
acids, such as hydrochloric or nitric acid. 

On gently heating it turns brown, and then violet; in the presence of air it 
burns with a bluish flame, leaving only about 0-1 per cent. of ash. This is the usual 
method of determining its purity. 

Vermilion, as it comes on to the market, is rarely if ever adulterated. 


z 


120 THE CHEMISTRY OF PAINTS 


Vermilion Substitutes or Vermilionettes are, however, sold in very large 
quantities. These are made by precipitating alizarine, eosine, Para reds, etc., on 
to barytes, or a mixture of barytes and orange lead (see Lakes, Chapter XIII). 
They may readily be identified by— 

(1) Ashing or igniting the sample and examining the residue. 

(2) Warming with alcoholic potash solution and filtering, whereby the dye-stuff 
is extracted. 

Vermilion is still a favourite pigment with artists. 

It is used for colouring shellac and also in printing inks for special purposes. 

Analysis of Vermilion.—A complete analysis of vermilion is very rarely called 
for, and in most cases it is quite sufficient to take 1 gm. and ignite im a crucible in 
a muffle furnace. Any ash more than 0:2 per cent. indicates adulteration. 

If any ash be present, then boil with alcoholic potash and filter. If the filtrate 
is coloured, due to the presence of dye-stufis, then proceed as described under the 
analysis of Lake Pigments (Chapter XIII.). 

Specification for Vermilion.—The vermilion must be equal in shade and 
brightness to that of the standard, and be fine in texture. 

It must consist of mercury and sulphur only, and on ignition leave less than 


0-2 per cent. of ash. 


ANTIMONY VERMILION 
(Antimony Orange, Antimonzinnober.) 


Antimony orange is a compound of antimony and sulphur, and has the formula 
Sb,83. It is no longer used as a pigment in the paint industries, though a considerable 
amount is still used for colourimg indiarubber in the rubber industries. It is made 
in two shades, orange and red. 

The method used in the manufacture of this pigment consists in precipitating 
a solution of antimony chloride with a solution of hyposulphite of soda or lime at 
a temperature of about 70° C., and keeping at this temperature for two or three 
hours, with continual stirring, until the shade has fully developed. 

It can also be prepared by passing sulphuretted hydrogen through a solution 
of antimony trichloride, or a solution of tartar emetic :— 


ISbCl,+3H,S=—Sb,8,+6HCl. 


CHAPTER XI 
THE BROWN PIGMENTS 


THE range of brown pigments is small, the chief ones of interest being the umbers 
and the Vandyke browns, both of which are natural earth colours. 


RAW UMBER 
(Raw English Umber, Raw Turkey Umber.) 


This important earth colour is found in several parts of the country, also in 
France, Germany and America. The finest quality comes from Cyprus, and is 
known as raw Turkey umber to distinguish it from the poorer English umbers. 

Composition.—Its composition is somewhat similar to that of the ochres and 
siennas, but differs from them in that it contains a considerably higher percentage 
of manganese in the form of MnO, or Mn,O,. This earth is prepared for use as a 
pigment from the crude lump umber by the usual process of grinding and levigation. 

Properties and Uses.—Raw umbers have a warm reddish brown colour with a 
greenish undertone; this undertone is especially noticeable in the raw Turkey 
umbers, and is due to the higher iron and manganese content as compared with 
English umbers, which are dirtier and duller in tone. 

Raw umber is quite permanent, and mixes with all colours without change. 
It is very largely used as a stainer and tinter as well as a graining colour ; it is also 
extensively employed in the manufacture of brown paints. 

Raw umber paints work well under the brush, and owing to their manganese 
content dry off very hard and wear extraordinarily well. 


BURNT UMBER 
(Burnt Turkey Umber.) 


Burnt umber is prepared by roasting the raw umber over a slow fire at a dull red 
heat till the desired shade is obtained. By this means all the water is expelled and the 
umber acquires a warm dark reddish-brown hue, which is very much appreciated. 

This change of colour is practically due to the transformation of the brown 
ferric hydrate into the red ferric oxide. 

Burnt umbers differ in quality and hue from the raw earth inasmuch as they 
are a darker and warmer brown shade, and also more transparent. 

In addition to being used as stainers and tinters, and also in the manufacture 
of paints, a certain amount is used as a dryer in the varnish industry. 

121 


122 THE CHEMISTRY OF PAINTS 


ANALYSES OF RAw AND BurNtT UMBERS 


The following analyses by the author will indicate the average composition of 
these pigments :— 


1 2 3 
Raw Turkey Burnt Turkey Raw English 

Umber. Umber. Umber. 
Moisture : : : 5 3 2°31 0-55 ~ 1-85 
Loss on ignition . : . 16-64 7-80 15-54 
Silica (Si0,) . : ' : . 16°60 22-75 31-56 
Ferric oxide (Fe,05) : : ~  d9:95 49-8] 25-76 
Alumina (Al,O;) . : : : 4-60 1-89 9-45 
Manganese dioxide (MnO,) eee ols!) 12-00 6-42 
Calcium oxide (CaO) ‘ ; : 7-10 4-80 8-35 

98-70 99-60 98-93 








SCHEME FOR THE ANALYSIS OF UMBERS 


Note.—This scheme is also applicable for all earth colours such as siennas, 
ochres, etc. 

(1) Movrsture—Heat 2 gms. at 110° C. until constant. Loss in weight equals 
hygroscopic water (moisture). 

(2) Combined Water.—Ignite the above dried sample in a platinum crucible 
over a low Bunsen burner. Loss in weight equals combined water. 

Note.—Organic matter, and carbonates, would render the result inaccurate 
unless allowed for, hence this result is often expressed loss on ignition. 

(3) Insoluble Matter (Silica, Barytes, etc.).—Digest 1 gm. of sample with 
50 c.cs. concentrated hydrochloric acid and take down to dryness on the hot plate 
to render the silica insoluble. Filter, ignite and weigh. The residue, which should 
be white, consists of silica. Test with platinum wire to make sure no barytes is 
present. If barytes is present it may be estimated by removing the silica with 
hydrofluoric acid in the usual way. 

(4) Ferric Oxide (Fe,O3).—Make up the filtrate to 250 c.c. and pipette out 50 c.c. 
into a basin and estimate the iron in the ordinary way by titration with standard 
bichromate of potash solution (see under Analyses of Iron Oxides, Chapter X.). 

(5) Alumina (A1,0;).—Take 50 c.c. of the 250 c.c. in (4), dilute, add a little solid 
ammonium chloride and ammonia, and bring to the boil. Filter and wash. If 
manganese is present then dissolve the precipitate of iron and alumina thus obtained 
and re-precipitate, thus ensuring that any manganese that may have come down 
in the first precipitation is separated. Add washings and filtrate to the first filtrate. 
Dry, ignite and weigh; equals alumina and iron. Alumina is got by subtracting 
weight of iron obtained previously volumetrically. 

(6) Manganese.—Take 0-5 gms. of the sample and add 30 c.c. concentrated 


BROWN PIGMENTS 123 


hydrochloric acid, and boil till the residue is white, indicating that all the manganese 
and iron has been dissolved. Then add a little sulphuric acid and evaporate down 
till all the hydrochloric acid is expelled, as evidenced by the evolution of sulphur 
trioxide fumes. 

Cool, dissolve in a little water, and warm up till all the ferrous sulphate is 
dissolved. Bring to the boil and add zinc oxide paste (made by mixing pure zinc 
oxide in water) a little at a time. Keep adding the zinc oxide paste, while stirring, 
till all the iron is precipitated and some zinc oxide is left over. 

Filter, wash well, and to the filtrate add about 3 gms. of acetate of soda. 
Bring to the boil and add a slight excess of bromine water. Boil well and then 
allow the precipitate of manganese to settle. 

Filter, wash well with boiling water, and ignite; equals MnO,. If preferred 
the manganese may be estimated volumetrically by dissolving the manganese 
precipitate in dilute sulphuric acid and excess of oxalic acid and titrating back 
with standard permanganate solution. The volumetric method is very convenient 
where a large number of manganese determinations have to be made; it is also 
more accurate, as in the gravimetric estimation there is always some difficulty 
because the manganese precipitate adheres very firmly to the sides of the beaker 
and is very troublesome to remove. 

(7) Calcium (CaO).—To the filtrate from the iron and alumina (5) add ammonium 
sulphide. Warm and filter off the manganese. Wash well and precipitate the 
calcium with ammonium oxalate. Filter and ignite ; equals CaQ. 

(8) Magnesiwm.—Precipitate by adding soda phosphate in the usual way. 


SPECIFICATION FoR Burnt TurKEY UMBER 


1. The burnt Turkey umber shall be a genuine natural Cyprus umber, calcined 
to the same shade and depth of tone as the standard sample, and be free from all 
added matter such as barytes, silica, Paris white, etc. 

2. It shall be finely levigated and free from all coarse particles. 

3. It shall contain not less than 36 per cent. of iron estimated as Fe,O3. 

4. It shall not contain more than 1 per cent. of moisture and 2 per cent. of 
matter soluble in water. 

5. On reduction with 10 parts of zinc oxide in linseed oil the resultant shade 
shall be equal to that of the standard similarly reduced. 

The specification of a raw Turkey umber is as above, except it must be a 
genuine raw levigated Cyprus umber and contain not less than 30 per cent. Fe,0s. 


VANDYKE BROWN 
(Cassel Brown, Cologne Earth.) 
Vandyke brown derives its name from the great Flemish painter, who was 


particularly partial to the use of brown in his pictures. 
At the present time far and away the best Vandyke brown comes from Germany. 


124 THE CHEMISTRY OF PAINTS 


It is manufactured from natural deposits of a brown earth, rich in organic matter, 
by very carefully heating so as to drive off all excess of moisture. 

Sometimes various substitutes are sold as Vandyke brown which are very 
inferior as regards shade, and simply consist of mineral blacks mixed with ochre 
and umber to tone them up. 

Properties and Uses.—Vandyke browns have a warm reddish-brown shade, 
rather transparent, and are of a woolly texture. It is sold ground in oil, in water, 
and in turpentine, and is largely used as a stainer and in graining work. It is a 
favourite water colour with artists, and is fairly permanent as such, but more so 
when ground up in oil. 

Composition and Analysis.—As already mentioned, the composition of true 
Vandyke brown is mainly organic, and on ignition it only leaves about 10 per cent. 
of residue. 

An analysis of two German Vandyke browns by the author gave the following 
results :— 








1 2 
Loss on ignition . . 90°34 Organic matter. » 92-20 
Ash 1 A : : 9-66 Silica . : . d 2-80 
Tron and alumina . p 3°30 
Lime . : ; ; 2-30 
100-00 100-60 








Soluble Vandyke Brown.—When treated with alkalies Vandyke brown is 
rendered soluble, and in this form is largely sold as Vandyke crystals ; the latter, 
which are soluble in water, are used in making walnut water stains. 


SEPIA 


This dark-brown colouring matter is obtained from the ink-bag—a weapon 
of defence—of the cuttle-fish (Sepia officinalis, Loligo tunicata), which abounds in 
the Mediterranean and Adriatic, and also off the coast of China. 

This pigment is of a dark brown colour, and partakes of the character of a weak 
organic acid. It is prepared by dissolving the dried ink-bags from the cuttle-fish 
in a dilute alkali, straining and precipitating the colour with dilute hydrochloric 
acid, then washing and drying. 

Sepia is used as a water colour by artists and is fairly permanent. 

The other brown pigments, such as Prussian brown, bistre, Cappagh brown, 
are no longer of any general interest, and nothing is to be gained by describing 
them in any detail. 


1 The ash consisted of silica, iron and alumina, with a proportion of carbonates of soda 
and lime. 


CHAPTER XII 


THE BLACK PIGMENTS 


TuE black pigments that are in general use in the paint industry may be divided into 
two classes :— 

1. The black earth pigments, which are prepared for use from naturally 
occurring substances such as coal, mineral black, graphite, etc., by a process of 
grinding and levigation. 

2. The artificial black pigments such as lamp black, vegetable black, gas carbon 
black, ivory black, vine black, and others, which are obtained by imperfect combustion 
or charring of organic matter. 

All organic black pigments contain carbon as their essential constituent, and 
while all these substances are said to be of a black colour, they naturally vary con- 
siderably both in shade and strength according to the amount of amorphous carbon 
they contain. Thus vegetable black, which is obtained by the imperfect combustion 
of oil, is practically pure amorphous carbon, and possesses far and away the best 
covering power and strength of all the black pigments in common use. Natural 
mineral black on the other hand often contains only about 30 per cent. of carbon, 
and is comparatively poor as regards tinting strength and covering power. 

Carbon, as is well known, occurs in three allotropic modifications :— 

(1) The colourless, highly refractive crystalline diamond, which is one of the 
hardest substances known, and has a specific gravity of 3-5. Lavoisier, in 1772, was 
the first to show that the diamond was a combustible body, and that it yielded 
carbon dioxide; while Davey, in 1814, showed that carbon dioxide was the only 
product of its combustion, and hence proved that the diamond was pure carbon. 

(2) The soft, shiny, greyish-black amorphous graphite, also in the crystalline 
variety as a soft lamellar, scaly or flaky structure; its specific gravity is about 2°5. 

(3) The non-crystalline or amorphous form of carbon, which may be obtained 
by the decomposition of a great variety of carbon compounds, such as, for example— 
the most ancient of all—the conversion of wood into charcoal. 

Carbon is an ideal pigment on account of its stability ; it is unaffected by light 
and air. Acids and alkalies have also no action upon it; in fact, it is resistant to 
all agencies, and can only be destroyed by the aid of very high temperatures in the 
presence of air (combustion). 

It may be noted here that paints made from carbon blacks, both natural and 
artificial, are rather slow drying; hence these paints require more than the average 
amount of driers. 

125 


126 THE CHEMISTRY OF PAINTS 


The many methods in use for the production and preparation of these blacks, 
which are suitable for use as pigments in the colour industry, may now be described. 


THE BLACK EARTH PIGMENTS 
MINERAL Buacks 


True mineral black is a dry shale which occurs fairly widely distributed in 
nature. It is found in Spain, Germany, Italy, and many other places. 

It is, as a rule, composed of about 30 per cent. carbonaceous matter and 70 per 
cent. of siliceous matter, though occasionally samples are met with having a much 
higher carbon content. 

Many other forms of mineral black come on to the market, such as coal black 
(which is prepared from waste coal dust), slate black, and so on. Some of these are 
toned up by additions of crude charred matter, such as ground charcoal, lamp 
black, or other crude prepared blacks. 

Mineral black is largely used on account of its cheapness in the manufacture of 
common black paints, sometimes a small amount of vegetable or carbon black being 
added to help to deepen the colour. 

The following results obtained by igniting three different samples of commercial 
mineral blacks will indicate the variability of this pigment :— 








1 2 3 
Mineral Black. Coal Black. Slate Black. 
Loss on ignition (carbon) ¢ 30°35 76-99 27-95 
Ash . : é : , 69-65 23-01 72:05 
100-00 100-00 100-00 





Biack OxiIpE oF [Ron 


This black oxide pigment is a triferric tetroxide, and has the formula Fe,0, ; 
it occurs naturally as the mineral magnetite, and contains over 90 per cent. FeO, 
(see Iron Oxides, Chapter X.). | 


GRAPHITE 
(Plumbago, Black Lead, Reiss Blei.) 


Graphite is widely distributed in different parts of the world. Large deposits 
are found in Ceylon, Madagascar, India, Siberia, United States, Canada, Bavaria, 
Bohemia, and other places. Big quantities of very fine black lead were formerly 
obtained from Borrowdale (Cumberland), but these deposits are practically worked 
out. Graphite also occurs in many specimens of meteoric iron. 

The composition of a natural graphite from California is shown by the following 
analysis :— 

Carbon. : . ; . 88-51 
Ashe : , 5 boy Bake 
Volatile matter . ‘ . 2°35 


BLACK PIGMENTS | 127 


Formerly graphite was supposed to contain lead; hence it was frequently 
called black lead and plumbago. 

Artficial Graphite—Molten iron dissolves considerable quantities of carbon, 
particularly if much silica be present. On cooling, part of this carbon is deposited 
in the form of black shiny crystals of graphite. Occasionally large quantities* of 
graphite are found deposited in this way in iron-smelting furnaces; the name 
“ kish ” has been given to such deposits. 

Graphite is also formed when charcoal or coke is heated to a very high tempera- 
ture in the electric furnace out of contact with air. 

_Acheson’s graphite is made at Niagara Falls by grinding coke with coal tar, 
molasses, etc., then heating in closed electric ovens to an extremely high temperature. 
It is then finely ground for use as a pigment. 

Natural Graphite-—The great bulk of the graphite at the present time is obtained 
from the naturally occurring deposits in America, Ceylon, Bohemia, and other parts 
of the world. 

The method simply consists in either a dry grinding of the selected material, 
or, in the case of the cruder sorts, levigating and grinding. 

Properties and Uses.—The specific gravity of graphite varies from 2 to 3. It 
occurs in two forms—crystalline and amorphous. 

Graphite is a soft, shiny, greyish-black substance, which is smooth and soapy 
to the touch. It is a good conductor of both heat and electricity. 

On ignition in oxygen, graphite burns, forming carbon dioxide, and leaves an 
ash consisting of silica, alumina, and oxide of iron. When rubbed on paper, it 
leaves a black mark on account of its softness; hence the name “ graphite’ from 
the Greek “ to write.” 

Graphite is largely used in the manufacture of lead pencils. For this purpose 
the natural graphite is purified by grinding, and carefully washed free from gritty 
matter. It is then mixed with the finest washed clay, and the pasty mass forced 
by hydraulic pressure through perforated plates. 

On account of its refractoriness graphite is also largely used in the manufacture 
of plumbago crucibles ; in addition, it is employed as a lubricant, in battery plates, 
in anti-corrosive paints, in polishing gunpowder, in stove polish, and for many 
other purposes, too numerous to mention here. 

As a pigment graphite has come very much to the front of late years, on 
account of its admirable anti-corrosive properties, and large quantities are used 
nowadays in the preparation of the many graphite anti-rust paints that are put 
on the market, and sold in very large quantities for painting iron structures, such 
as bridges, etc. (see Anti-Corrosive Paints, Chapter III.). 

Graphite can be readily detected in a paint or pigment by simply rubbing a 
portion between the fingers, when it leaves a characteristic black shiny mark. 


128 THE CHEMISTRY OF PAINTS 


VEGETABLE BLACK 
(Lamp Black, Soot, Lampenruss.) 


The finest quality of vegetable black, which is nearly pure amorphous carbon, 
is obtained by burning mineral oils. 

Process 1.—The process of manufacture is quite simple. Mixtures of mineral 
oil and mineral oil residues are fed from a tank or a constant level cistern into a 
series of lamps provided with burners and wicks, somewhat similar to the ordinary 
household lamp, by means of communicating pipes. 

A large sheet iron funnel is placed over the flame so as to limit the air supply and 
just allow the oil to burn gently, and thus produce the maximum amount of soot. 

From this funnel there is a slanting iron pipe through which the products 
of combustion and soot pass intoa brick chamber. This chamber is connected 
with a series of cylindrical hemp or jute bags, through which the products of com- 
bustion and lighter soot pass and collect, the last bag being connected with the 
chimney. The bags can be opened at the bottom to remove the soot that collects 
from time to time. 

The black that collects in the bags at the end of the series is the lightest and 
freest from oily residues and constitutes pure vegetable black of the finest and lightest 
quality. 

The yield of black from this process is only about 20 per cent. of the oil con- 
sumed, hence it is a costly process. 

Process 2.—The great bulk of the vegetable and lamp blacks which come on 
to the market at the present time is obtained by the incomplete combustion of such 
carbonaceous materials as rosin, tar, tar oils (creosote, etc.), naphthalene, mineral oil 
residues, pitch, and so on. 

The process consists in charging a large movable, or fixed cast-iron pan with 
the oily or solid (usually a mixture of both) materials, and heating them up to the 
temperature of ignition, when they are set alight. 

Several of these pans are connected with large iron pipes provided with a series 
of dampers for regulating the air supply leading into a long brick chamber about 
90 ft. long by 10 ft. wide by 10 ft. high. The chamber is divided into compart- 
ments, an upper and a lower; each of these is subdivided into about six sections 
by means of brick walls three-quarter way up, so arranged that the products of 
combustion have to travel from section to section through the chamber till finally 
they come to a flue connected with the chimney. 

The black gradually collects in the various chambers; the coarser blacks con- 
taminated with oily particles being caught in the first chamber where they are collected 
and burnt over again. The finest and lightest blacks collect in the upper end 
chambers. 

As a rule two qualities are collected: the finest and lightest in the end chambers— 
which is known as vegetable black ; and the somewhat denser and heavier particles, 
known commercially as lampblack, in the other chambers. 

The chambers are emptied from time to time by workmen who go in provided 


BLACK PIGMENTS 129 


with special clothing and respirators, and rake and brush out the accumulated black, 
which is packed straight into casks or bags. 

During the process of combustion great care must be taken to regulate the heat 
and the air supply, for if there is too much air the combustion is carried too far, with 
considerable loss of black, and if, on the other hand, the temperature is allowed to 
get too high, then considerable amounts of oily material are votalilised or distilled 
over, spoiling the black formed in the earlier chambers. 

Properties and Uses.—Vegetable black is one of the purest and lightest forms 
of amorphous carbon that is produced commercially. On ignition it leaves less 
than 0-1 per cent. of ash. Its specific gravity is 1-7. 

Lamp black is not quite so pure, and leaves an ash often as high as 0-8 per 
cent.; and as we have already mentioned, it is considerably denser and heavier 
than vegetable black. The lamp black sold in packets on ashing is often found 
to give as much as 25 per cent. or more of residue. The latter cannot be described 
as pure lamp black, but a lamp black to which considerable quantities of other 
matter has been added as an adulterant. 

Vegetable black is of a deep black shade, which on reduction with white lead 
gives a bluish-black tint. 

Lamp black is not quite such an intense black, and is of a brownish-black colour. 

Vegetable black is exceedingly fine and soft in texture, and has very great 
covering power and strength. It requires rather more than its own weight of oil 
to grind into a stiff paste. It floats on water without mixing, a circumstance due 
to its gaseous and oily content. 

Largely used in paint, vegetable black is also employed as a tinter for various 
grey and slate-grey paints. It is also largely used in the manufacture of flat black 
paints and enamels, also for printing inks. 

Specification for Vegetable Black.—1. The black shall consist of pure amorphous 
carbon only, and be equal in shade and density to the standard sample. 

2. On ashing 1 gm. there must be less than 0-5 residue. 

3. On extraction in a Soxhlet apparatus with ether, it must not yield more 
than 0-5 per cent. of oily residue. 

4, On reducing one part of black with 100 parts of zinc oxide in linseed oil, 
the resultant shade shall be equal in tone and shade to that of the standard 
similarly treated. 

5. It shall not contain more than 0°5 per cent. of moisture. 

Nore.—tThe specification for a lamp black should as a rule allow an ash content 
of more than 5 per cent. 

Cuinese INK 
(Indian Ink, Japanese Ink, Encre de Chine, Chinesische Tusche.) 

This ink is essentially a very fine lamp black. The Chinese have prepared it 
from very ancient times by the imperfect combustion of oil in earthenware lamps. 
The soot formed is mixed up with fish-glue size, scented with musk or camphor, 
and moulded into sticks and dried. The ink is soluble in water and gives a bluish- 
black colour, which is quite permanent. 


130 THE CHEMISTRY OF PAINTS 


Carson BLAck 
(Gas Carbon Black, Gas Russ.) 


This black comes exclusively from America, and is now used in large quantities 
in the paint and printing-ink trades. 

As a rule it is sold in wooden cases of 1874 Ibs., and containing 15 paper bags, each 
weighing 123 lbs. It is sold under the different brands or marks of the various makers. 
The quality is, as a rule, about the same. There are, however, one or two particular 
brands which are about 24 times lighter or bulkier than the usual gas carbon blacks, 
and are sold for special purposes, such as the making of special printing inks. 

Carbon black is obtained in America by burning the naturally occurring gases 
which come from the earth in such localities as Pennsylvania, Ohio and Virginia. 
It is calculated that it takes about 4000 cubic feet of natural gas to produce 1 lb. of 
carbon black. 

The process of manufacture is very simple, and is as follows :—The natural gas 
is conducted through iron pipes to the brick chambers in which the gas is burnt. 
The flame from the ignited gas is made to impinge on to revolving drums, on which 
the carbon is deposited. As the drum revolves it automatically comes into contact 
with fixed sweepers which remove the carbon black deposited, which is subsequently 
collected. 

The natural gas yields such a fine black that it needs no purification. As fast 
as it is produced it is carried away by moving hoppers and packed by machinery 
into bags ready for use. 

Properties and Uses of Carbon Black.—Carbon black is of a very deep black colour, 
and is more granular and much harder in texture (and therefore requires much more 
grinding) than vegetable black. It is also considerably denser than the latter, and 
has a specific gravity of 1-85 to 2-10. 

It is a pure amorphous carbon and leaves no ash on ignition. It is largely used 
in the paint and printing-ink trades. 

Carbon black, when analysed, is found to consist of from 85 per cent. to 95 per 
cent. of amorphous carbon, from 1 per cent. to 7 per cent. of water, from 0-5 per cent. 
to 0-8 per cent. of hydrogen, and from 2 per cent. to 8 per cent. of oxygen (which 
is present partly in the H,O of the water content). 

Specification for Carbon Black.—It must be a pure gas carbon with not more 
than 0-5 per cent. ash, and equal in shade and strength to the standard sample. 


Ivory Biack 
(Bone Black, Beinschwarz, Noir d’Ivoire.) 


Ivory black was formerly made by charring waste cuttings of ivory in closed 
vessels, then grinding and washing and drying the resulting black residue. 

At the present time ordinary bones are used, or more generally, glue works’ 
residues, that is, bones which have been digested so as to remove the fat and glue 
from them. 


BLACK PIGMENTS 131 


The dried bones are crushed and packed into crucibles in order to exclude the 
air; they are then piled one on the top of the other in a sort of muffle furnace and 
heated for several hours till all the volatile matter has been driven off, leaving a black 
mass of bone charcoal behind. 

In more modern works the process is carried out in large iron retorts so that 
the products of distillation—ammonia, Dippel’s oil, or bone oil—can be collected 
and recovered. 

The “ char” or bone black that is left behind is ground, either coarsely if for 
sugar-refining purposes (i.e. as a decolorising agent), or else extremely finely for 
use as a pigment. 

Properties and Uses of Ivory Black.—Ivory black is of a bluish-black colour 
and fairly smooth in texture. It is considerably denser than carbon black. Its 
specific gravity is about 2-68. Ivory black contains on an average 10 per cent. 
of carbon, 84 per cent. calcium phosphate and 6 per cent. calcium carbonate. It 
is used ground in oil as a paint and tinter, and also in the printing and ink trades. 
Ground in turpentine and gold size it is employed by coach-builders as a body colour. 

It is also sold under the names of animal black and jet black. 

If the calcium phosphate and carbonate content be removed by digesting with 
hydrochloric acid, a fine black is obtained which commands a fancy price under the 
name of “ black toner.” 

Like all the carbon colours, it.is absolutely permanent and unalterable under 
all ordinary conditions. 

It is often sold in the form of drops known as “ drop ivory black.” 


Vine Buack 
(Rebenschwarz, Noir de Vigne, Frankfort Black, German Black.) 


True vine blacks in their purest form are prepared by carbonising grape husks, 
vine twigs, washed wine lees, andso on. Other non-resinous woods and woody tissues 
are now also largely used, such as cocoanut shells, cork cuttings, twigs of beech and 
other woods, but the quality of the black is not equal to that of the true vine blacks. 

The method of producing these blacks consists simply in packing the raw material 
in crucibles made of clay or iron, provided with luted covers to exclude excess of 
air, but at the same time allowing the products of the partial combustion or charring 
process to escape. 

These crucibles are heated in a kind of muffle furnace, and when the issuing 
gases and moisture have ceased, the furnace is allowed to cool down and the contents 
of the crucibles are emptied out and recharged for the next operation. 

This black is now often made by charring the woody materials in large retorts 
and collecting the products of distillation. This is especially the process in use 
for producing the cruder forms of vine black, which are really simply wood charcoals 
or charcoal blacks. The black residue is next very carefully washed, ground, dried 
and sieved so as to make it suitable for use as a pigment. 

Properties and Uses.—Vine black is a beautiful bluish-black pigment, with great 


132 THE CHEMISTRY OF PAINTS 


depth of tone. On reduction with white it gives bluish-grey shades. It is largely 
used in the printing-ink trade and as a tinter for paints. Like all carbon blacks, 
it is quite permanent. Unfortunately at the present time large quantities of char- 
coal blacks are sold as vine blacks, and tinted up with Prussian blue so as to give 
the characteristic bluish-black colour. 

Vine black makes a very good pigment for use as a water colour for artists. 

It might be mentioned that this black is sometimes sold under the names of 
Frankfort black or drop black in the form of cones or drops. These drops are 
produced by mixing the black with a solution of glue and squeezing the pasty mass 
through tubes on to a board in the form of drops, then drying at a low temperature. 
More often however the drop black that comes on to the market is simply bone black 
made up into drops or cones, and may be readily identified by the large residue 
consisting of calcium phosphate which it leaves on ignition. 


GENERAL SCHEME FOR THE ANALYSIS OF BLACK PIGMENTS 


1. Moisture—Weigh out 2 gms. on a watch-glass and heat at 105° C. till 
constant. Loss in weight equals moisture. 

2. Oily Matter—Extract 2 gms. in a Soxhlet’s apparatus with ether and weigh 
the oily residue thus extracted. 

3. Ash.—Weigh out 1 gm. into a crucible and ignite by strongly heating over 
a Bunsen burner until constant in weight. The residue may be quantitatively 
analysed if required, though as a rule a qualitative analysis is quite sufficient for 
most purposes. 

4. Carbon.—This is obtained as a rule by difference, by adding together the oil, 
moisture and ash, and subtracting from 100. 

The following analyses by the author will give an indication of the average 
composition of the various blacks that are in general use as pigments in the paint 
and printing-ink industries :— 

Drop Ivory Black. Vegetable Black. Carbon Black. 


























Moisture . E 0-12 0-35 0-11 
Oil . . . a 0-21 
Ash 1 : : 81-00 r a 
Carbon . : 18-88 99-44 99-89 
100-00 100-00 100-00 
gre eat Vine Black. Finest Lamp Black. 
Moisture . ; 0-45 0-15 0-46 
Oil . ; ! 0-45 Ae 0-82 
Ash 2 i / 60-20 10-38 0-38 
Carbon . : 38-90 89-47 98-34 
100-00 100-00 100-00 











1 The ash is chiefly calcium phosphate. 2 The ash is silica with traces of iron and alumina. 


CHAPTER XIII 
LAKES AND LAKE PIGMENT COLOURS 


LAKES FROM NATURAL COLOURING MATTERS 


Lakes are obtained by precipitating or fixing an organic dye-stuff on to an 
inorganic base, and are used in enormous quantities in the paint, printing ink and 
wall paper industries. 

This class of pigments was used by the early Italian painters under the name 
of “lacca,” which was obtained by precipitating certain natural dye-stuffs or lacs 
with tin and alumina compounds. Hence the derivation of the word. 

The earliest lakes were, of course, all made from dyes extracted from the 
various natural occurring plants, woods, insects, etc., such as madder, logwood, 
Brazil wood, Persian berries, cochineal, indigo, and many others; but during the 
last half-century, owing to the enormous strides made in the development of the 
synthetic aniline dye-stufis, especially in Germany, they have gradually fallen into 
disuse, and are now only employed for special purposes. 

True lakes may be defined as transparent colours produced by precipitating 
the colouring matter (either natural or synthetic) on to a base of hydrate of alumina. 

In recent years, however, this definition has become more generalised, and we 
have lakes on an alumina blanc-fixé basis. Further, to get more body for use in 
the enamel and paint industry, additions of such bases as barytes, zinc oxide, orange 
lead have been made to the true lakes, and thus we have what we may term the 
lake pigment colours, which possess very considerable body and covering power. 


COCHINEAL LAKES 


CaRMINE LAKE, Crimson Lake, Munico Laks, VIENNA LAKE, 
VENETIAN LAKE, SCARLET LAKE, PURPLE LAKE, ETC. 


The raw material for the manufacture of cochineal or carmine lakes is the 
coccus cacti insect, which is indigenous to Mexico and Central America. These 
insects are collected from the trees on which they live by the natives, and are 
killed by dry heat in kilns. The dried insects come into commerce, packed in bags 
of about 160 lbs. each, under the name of Cochineal. 


Crimson Lake 
The method used on the large scale for the production of this lake consists in 
digesting the powdered cochineal in a large copper—through which live steam is 
133 


134 THE CHEMISTRY OF PAINTS 


passed—with a weak solution of carbonate of soda. After two hours’ boiling the 
infusion is strained off into a wooden precipitating beck, and struck down by 
running in the requisite amount of 5 per cent. solutions of alum and cream of tartar. 

Sufficient freshly precipitated and well-washed hydrate of alumina (White 
Base, see Chapter VI.) is then added in order to produce the required shade. The 
lake is washed three times, filtered and dried at a low temperature. 


SCARLET LAKES 


are prepared in a similar way to crimson lakes, but a certain proportion of genuine 
vermilion is added along with the hydrate of alumina so as to get the desired shade. 


PurRPLE LAKES 
as crimson lake, with the addition of lime to produce the deep purple tone required. 


CARMINE LAKES 


The cochineal extract in this case is precipitated on to the alumina base as 
already described, but with the addition of chloride of tin. 

Properties and Uses.—The cochineal lakes are used for colouring food and in 
cosmetics, but mainly in the preparation of fine coach body colours. They are 
gradually being superseded by the more permanent lakes made from the synthetic 
aniline dye-stufis. 


Mapper LaKksEs 


These lakes were formerly made by extracting the dye from the madder roots 
and precipitating with a solution of alum. They have now been replaced by lakes 
made from synthetic alizarine (see Alizarine Lakes). 


Rost PInk 


Brazil wood (lima wood or red wood) is digested in a boiler under pressure 
with a 5 per cent. solution of soda ash. The extracted liquor is run through sieves 
on to a base consisting of equal parts of Paris white and terra alba, then struck 
down with a weak solution of alum. 


Dutcu PInK 


Quercitron bark, indigenous to Brazil, is soaked for about ten days in a cold, 
weak solution of soda ash till the greater part of the colouring matter is extracted. 
The extracted liquor is decanted off and struck down on to a base of Paris white 
and terra alba with a weak solution of alum. 

Properties and Uses.—Rose pink and Dutch pink are not much used nowadays 
owing to their fugitive and weak nature. They are used as toners (e.g. Dutch pink 
in Brunswick greens), also by scenic painters. 

These natural dye-stuff lakes very often come on to the market in the form of 


LAKES AND LAKE PIGMENT COLOURS 135 


cones or drops. These drops or cones are produced by squeezing through funnels 
the pasty lake to which a little size solution has been added to act as binder. 


Buack LAKE 


is made from logwood extract (hematein), by dissolving in a strong hot solution 
of soda ash, boiling with ferrous sulphate and bichromate of soda, then precipitating 
with sulphate of alumina. 


LAKES FROM SYNTHETIC DYE-STUFFS 


Historical.—At the present time the use of synthetic coal tar dye-stufis in the 
manufacture of lake and lake pigments has developed to an enormous extent. 

The founder of the synthetic coal tar dye-stuff industry, W. H. Perkin, laid 
down works for the manufacture of the first true aniline colour (mauve) at Greenford, 
near London, in 1856. He prepared mauve or mauvein (Perkin’s violet), C,,H,;N,Cl 
or (C,,H,;N,).5O,, by the action of potassium dichromate on aniline obtained from 
coal tar. After this discovery a large number of chemists in England, France and 
Germany began to investigate the synthesis of colouring matters from coal tar. 

In 1859 a French chemist, Verguin, discovered magenta (fuchsine), which was 
shown by A. W. Hofmann to be rosaniline hydrochloride :— 


an: H,(CH,)NH, 
NH, 
aie H,NH,Cl 


This discovery was closely followed by Hofmann’s violet, Nicholson’s blue, methyl 
violet and methyl green, and aniline black. In 1868 Perkin in England, and 
simultaneously Graebe and Liebermann in Germany, produced alizarine (the colouring 
principle of madder) from anthracene. The production of this synthetic dye-stuff 
was of immense importance, and its manufacture very soon displaced the natural 
product. 

In 1874 A. Baeyer and Caro prepared fluorescein and eosin (tetra-brom 
fluorescein) by the interaction of phthalic anhydride with resorcinol, brominating 
the fluorescein to produce eosin. 

If instead of phthalic anhydride, the di- and tetra-chlor substitution products 
are fused with resorcinol there is obtained in the phthalic acid residue, the di- and 
tetra-chlor fluoresceins, from which halogen substitution products, nitro-derivatives, 
ethers, etc., are produced, such as phloxine (dichlor-tetra-brom fluorescein) and 
rose Bengal. 

Since 1887 the phthaleins have been on the market under the name of 
rhodamines, which are prepared in a similar way to that of fluorescein, except that 
instead of resorcinol, m-amido phenol, a-amido phenols substituted by alkyls in 
the amido-group are used. Rhodamine B being a diethyl (phenyl- etc.)-m-amido 
phenol phthalein. 

Otto Fischer in 1877 discovered malachite green or bitter almond green by beating 
together dimethyl aniline and benzaldehyde with zinc chloride and oxidising the 


K 


136 THE CHEMISTRY OF PAINTS 


leuco base thus formed. If, instead of dimethyl aniline, diethyl aniline is used 
brilliant green is produced. 

Peter Griess, in 1866, discovered the diazo reaction and thus laid the 
foundation for the production of the insoluble azo and diazo colours which are one 
of the most important group of colours from which lakes and lake pigments are 
now obtained. 

The list of colours of this group is immense and is increasing year by year as 
fresh applications of its derivatives are being investigated. To this class belong, 
for example, the Para reds, Lithols, Scarlets, Ponceaus, Bordeaux, to mention only 
a few examples in illustration of the immensity of the range of colours that are now 
being produced based on this reaction. 

In 1880 Baeyer patented his process for the manufacture of artificial indigo, 
and by this process—modified and improved by other chemists such as Heumann, 
Sandmeyer, etc.—the Associated Aniline Companies of Germany (comprising the 
Badische Aniline Soda Fabrik, Meister Lucius & Brunning, etc.), manufacture 
yearly 95 per cent. of the total indigo consumed. There can be little doubt that 
it is but a question of time when the synthetic product will completely displace 
the natural indigo just in the same way that synthetic alizarine has displaced madder. 

Although, as we have already shown, the synthetic dye industry was founded 
in this country by Perkin in 1856, it was left to Germany to develop its immense 
possibilities. That she has been able to do so to such a remarkable extent is due 
mainly to the large number of highly trained scientific investigators available in 
that country, and in a lesser degree to the fact that the industry has received State 
aid and has been unhampered by excise restrictions in the use of pure alcohol. 

The formation of the British Dye-stufis Corporation in 1919, and its manufacture 
of many of the dye-stufis formerly imported from Germany, leads one to hope that 
this country will soon be self-supporting in the matter of the production of the 
synthetic dye-stufis required by our industries. 

Moreover, it is to be expected that with the large number of trained British 
chemists now engaged in the systematic investigation of synthetic dye-stuffs our 
dye factories will, in the course of time, bring out new and more permanent series 
of dye-stuffs, which will gradually replace those now in use. For the manufacture 
of lake and lake pigments the question of a large range of permanent dye-stufis 
suitable for the production of lakes of a bright and permanent character is of the 
utmost importance. But at the same time their cost must not be prohibitive. 

The manufacture and properties of the most important synthetic dye-stuff 
lakes used in the paint trade must now be considered. 


MANUFACTURE OF LAKE PIGMENTS FROM THE SYNTHETIC Dyz-STUFFS 


It is usual to group the synthetic dye-stufis employed in the manufacture of 
lakes and lake pigments according to their methods of precipitation as follows :— 


(A) Acid dye-stuffs precipitated with barium chloride. 
(B) Basic dye-stuffs precipitated with green earth (or white earth). 


LAKES AND LAKE PIGMENT COLOURS 137 


(C) Resorcin dye-stuffs precipitated with lead acetate or nitrate. 

(D) Diazo dye-stufis precipitated by diazotising or coupling. 

(#) Mordant dye-stufis precipitated on alumina such as Alizarine (formerly 
called adjective dye-stuffs). 

(f) Insoluble pigment dye-stuffs. 


The above classification is, of course, only a general one, and there are many 
exceptions as one would naturally expect. 

The Base-—The base or carrier for the dye-stuff must be very carefully chosen 
if the best results are to be obtained. For example, a dye-stuff struck on a base 
might be quite suitable for the manufacture of a paint, but unsuitable for use as a 
distemper or printing-ink colour. Hence the purpose for which the lake is going 
to be used must be carefully thought out by the lake manufacturer. 

Alumina.—The most suitable base for the manufacture of fine lakes for the 
printing-ink and wall-paper trades is alumina. The lakes formed on this base are 
of great transparency and brilliancy of colour. Blanc-fixe alone or in combination 
with alumina makes a splendid base of good covering power and of excellent fineness 
and texture. This base is very suitable for fine enamel colours. 

Barytes, being very cheap, is the base most commonly used. Care must be 
taken that it is fine and absolutely free from all grit. It must be of a good white 
colour, free from iron, and contain no acid or alkali. 

Terra alba, whiting, catalpo and china clay are also employed as bases according 
to their suitability for the special purpose for which the lake is intended to be used. 

Zine oxide, white lead, red lead and orange lead are used in conjunction with 
the above bases in special cases to act as toners where a particular tone or shade is 
required. 


A. Actb DYE-STUFFS PRECIPITATED WITH BARIUM CHLORIDE 


The manufacture of these lakes is carried out as follows :—The dye-stuff is dis- 
solved in boiling water, about 1 part dye-stuff to 100 parts water, then run into a 
large wooden vat provided with mechanical stirrers (see Fig 16). The base is next 
added and the stirrers set going, and when the right temperature has been reached. 
(about 80° C.), the requisite amount of the barium chloride (iron free) solution is 
run in till complete precipitation has taken place. 

To make sure that all the dye-stuff is precipitated, a portion is taken out and 
filtered to see that the liquor is free from any dye-stuff in solution. A quicker 
method is to take out a portion and spot it on filter paper and hold it up to the light. 
If complete precipitation has taken place, the wet spot round the lake will be 
colourless. The lake is well washed, filtered and dried at a low temperature. 

Examples.—The following examples will best illustrate how these lakes are 
produced. It must, of course, be understood that the examples given are only to 
be taken as a general indication of how the lakes are manufactured. The best 
results can only be obtained by studying each individual dye-stuff and finding out 
by experiment which is the most suitable for the particular purpose required. 


138 THE CHEMISTRY OF PAINTS 


Scarlet Lake 


(1) Brilliant Lake Scarlet G . : . 982 Ibs. (1: 100) 
Best barytes . ; : : Seo: ey 
Barium chloride . : ; vA gs AE es 


Yield . : . 5 ee oes 


Brilliant Turkey Red Lake 


(2) Brilliant Lake Scarlet G . ; . 20 lbs. 
Ponceau 2 R , : 5 . DF Ge 
Barytes : : ; ‘ 2 SUS aa: 
Barium chloride . : : 2; aS 


Niohie a> : : u Be ee 


(3) Blanc-fixe or best barytes . 112 Ibs. in 15 gals. water 


Brilliant Scarlet2R  . ; 5A, (1: 80) 
Barium chloride . : . 5d te) 


Yield . : . ety Lies 


Temperature of precipitation, 90°-95° F. 


(4) Precipitating Acid Dye-stuffs on Alumina—Blanc-fixe 


17-18 per cent. Sulphate of alumina . ‘ : . 12 the 
Soda ash . : 4 “ , eae 
Naphthol green B.. : : .\ ofa 
Barium chloride A , : . YS6ae 


Dissolve the sulphate of alumina in 120 gallons of cold water. 


Precipitate 


by adding the soda ash dissolved in 50 gallons of hot water. Stir and add the 
naphthol green B dissolved in 100 gallons of hot water; then add the barium 
chloride dissolved in 80 gallons of hot water. Wash, filter press and dry in the 


vacuum stoves. 


Note.—This naphthol green lake is very fast to light and lime, and hence is 


very largely used as a distemper colour. 


Alternative methods to this last formula are (1) to split the soda up into two 


parts, or (2) to split up the sulphate of alumina. 


1. 17-18 per cent. Sulphate of alumina . : bie 
Soda ash . , ‘ : oy gee 
Naphthol green Bs .. : . | 34 
Barium chloride . ; . 136 
Soda ash . ; , 5 o 


LAKES AND LAKE PIGMENT COLOURS 139 


2. 17-18 per cent. Sulphate of alumina . 5 baie: 
Soda ash ° ‘ : « * 60 
Naphthol green B. : . 34 
Barium chloride : : dee laG 
Sulphate of alumina . ; ng Bt 


The two-soda or two-alum process is very useful in those cases where difficulty 
occurs in striking down the dye-stuff completely by the direct process. Moreover, 
in some dye-stufis the resultant lakes are more brilliant and permanent than those 
obtained directly. 


B. Basic DYE-STUFFS PRECIPITATED BY GREEN Harty, TANNIN, TANNIN AND 
TARTAR EMETIC, KATANOL, ETC. 


The well-known capacity of green earth (or white earth) (see Chapter IX. to 
absorb many basic dye-stufis is largely taken advantage of in the production of 
lime fast colours, for use in distempers and kalsomines. The method is extremely 
simple and is as follows :— 


Example 1.—Green Earth Carrier. Example 2.—White Earth Carrer. 
Green earth : . 112 Ibs. White earth : : . 112 lbs. 
Malachite green . : ae Methyl violet B . ‘ , jae 
or Brilliant green crystals 2 ,, or Methylene blue B . ; yaa 


extra concentrated. 


The green earth or white earth is mixed into a thin sludge with cold water. 
The dye-stufis dissolved in 25-50 times their weight of hot water are run in, with 
continuous stirring, till all the dye-stuff is taken up. Filter press and dry. 

A good German green earth is capable of absorbing from 4 per cent. to 6 per 
cent. of its weight of basic dye-stuff, this being due to the formation of insoluble 
silicates with the dye-stuff. 


Example 3.—Precipitating by Tannin on China Clay 


China clay . A : 5 . 100 lbs. 
Auramine O . : i , 7 ea ss 
Tannin : ; : : s ss Wel 
Soda acetate 1} ,, 


Method.—Mix the china clay to a paste with 15 gallons of water. Add while 
stirring the 2 Ibs. of auramine O dissolved in 10 gallons of water. Then precipitate 
by the addition of 5 lbs. of tannin and 1} lbs. of soda acetate 1:10. Filter 
and dry. 

This precipitation is due to the formation of insoluble tannates with the 
basic dye-stufis. Temperature of precipitation about 150° F. 


140 THE CHEMISTRY OF PAINTS 


Example 4.—Precipitation with Tannin and Tartar Emetic on Hydrate of Alumina 


Hydrate of alumina ; : 5 - 100 lbs. 
Methylene blue . : 2 ; : DO ees 
Tannin (neutral) . : ; : = en ees 
Tartar emetic : 3 : ; on ees 


Method as Example 3. The tannin tartar emetic lakes are much faster and 
brighter than the tannin lakes. 


Tamol N (B.A.S8.F.) and Katanol (Bayer) 

The new precipitants tamol N (B.A.S.F.) and katanol (Bayer) have recently 
been introduced for producing lakes from the basic dye-stufis in place of tannin, 
and present many advantages over this substance. The lakes thus produced are 
not so spongy as the tannin lakes and are superior as regards covering power 
and fastness to light. 

Bayer’s katanol, a moss greenish powder smelling somewhat of iodoform, is 
a thiophenol, whilst the Badische tamol, which is a combination of formaldehyde 
and naphthalene sulphonic acid, is a liquid. Both require to be neutralised with 
soda ash before use. 

The following brief description of the manufacture of two katanol lakes will 
illustrate the method used in the production of these lakes (Bayer, 1921). 


Barytes Lake 


Barytes : : : ; . 100 lbs. 
Rhodulin blue 6 G a : ; ; PBA’ 
Katanol : 1 ,, +0°25 soda ash 
17-18 per cent eva of AHeAbY : +, dem 
The katanol solution is made as follows :— 
Katanol ; : , ; : . 100 gms. 
Soda ash : : 3 ‘ : . eee 
Boiling water ; : : 1 litre 


The dye-stuff is dissolved in fifty ¢ times its weight of hot water, run on to the 
barytes, stirring continuously. 

The katanol solution is then added till precipitation is complete. The excess 
of soda is neutralised by the addition of the requisite amount of a 10 per cent. 
solution of sulphate of alumina. 


Alumina Blanc-fixe Katanol Lake 


17-18 per cent. Sulphate of alumina ,  LOclbs a a 
Soda ash 5 , A ot cee 
Barium chloride  . 2S Se ee 

Wash the precipitate thoroughly, then add :— 
Victoria blue B : ye yg Uagee a ea 


Katanol solution . .) 13a, 


LAKES AND LAKE PIGMENT COLOURS 141 
This makes a very fine bright fast lake suitable for lithographic prints and 


paper staining. 

Other methods of precipitating these basic dye-stuffs which may be mentioned 
are by resin soap, Turkey red oil, casein, phosphate and silicate of soda, but we have 
not space to go further into these processes, which are only of minor importance. 


C. Resorcin DYE-STUFFS PRECIPITATED WITH LEAD NITRATE AND 
Leap ACETATE 


This group of colours consists chiefly of Hosine, Erythrosine, Phloxine and Rose 
Bengal. 

From these dye-stuffs are obtained the well-known vermilionettes and geranium 
lakes which are in large demand on account of the brilliance and beauty of their 
shades. Unfortunately they are not permanent, and hence are not suitable for 
use in paints or enamels which are made for outdoor work, being replaced for this 
purpose by the more permanent Para and. Lithol reds. 

Their method of preparation is exceedingly simple, as the following examples 
will show :— 


Example 1 
Barytes : : - : : . 100 Ibs. 
Eosine A 5 G : : ; : : 24 4 
Lead nitrate . : : : 5 , 7 ae 
Water . ; : : A ; : 2 gals. 


Dissolve the eosine in thirty times its weight of boiling water and run on to the 
barytes mixed to a thin paste with hot water, stirring continuously. Strike down 
the colour with a hot solution of nitrate of lead. 


Example 2 Example 3 
Barytes . ‘ : aeLUU Blanc-fixe q : LOU 
Red lead . : : . 100 Orange lead. ‘ - 100 
Eosine 2 G : é , 2 Eosine 1136. , : 3 
Phloxine . : : ; 1 Rose Bengal . : : 1 
Lead acetate . ' : 3 Lead acetate . P 4 4 


Precipitate as before. Temperature of precipitation 90° F. 


D. Tue InsoLtusLeE Azo anp D14azo DYE-STUFFS 


The discovery of the diazo reaction by Peter Griess in 1866 opened up the 
way for the production of an immense range of the most important dye-stufis for 
the manufacture of lakes of great brilliancy and permanency, such as the Para red, 
Lithols, Fast Scarlet R, etc. 

The formation of the dye-stuff consists, in its simplest form, in the diazotising 
the aromatic amines, and then coupling the diazo compound thus formed with a 
naphthol. 


142 THE CHEMISTRY OF PAINTS 


We will now give a few examples illustrating how this class of lakes is 
produced :— 


Para Red or Para Nitraniline Lake 


This is one of the simplest and earliest of the diazo colours, and its preparation 
will now be described in detail so as to give a clear insight into the basis on which 
this most important and valuable range of permanent reds is produced. 

(1) The Diazo Solution is made up as follows :— 

44 Ibs. 15 ozs. Para nitraniline are made into a paste with 8? gals. of cold water 
to which 119 Ibs. hydrochloric acid 32° Tw are added. 

After a further addition of 33 gals. of water—as cold as possible—24+4 Ibs. 
nitrite of soda just previously dissolved in 11 gals. cold water are poured in (in one 
portion) and then 88 lbs. 3 ozs. acetate of soda 1:3 is added. 

Then strain and fill up with cold water. 

(2) Naphthol Solution.—To 50 Ibs. beta naphthol or beta naphthol R pour 
110 gals. of hot water and 4 gals. soda lye 76° Tw. Then add 36 lbs. 53 ozs. 
soda ash and 22 lbs. Turkey red oil. 

Stir well until solution has taken place, fill up to 220 gals. and allow to cool. 

(3) Preciyntation of the Lake.—1102 lbs. barytes are stirred into the cooled- 
down naphthol solution. To this the diazo solution is slowly added whilst con- 
tinuously stirring. Allow to stand } hour, stirring occasionally. Pour the lake 
on to a filter, wash well with cold water, press and dry at about 120° F. 

Beta naphthol R gives lakes of a bluer tone than beta naphthol. Usually the 
diazo solution is cooled down with ice, hence the name ice colours given to 
these lakes. 

Properties and Uses.—Para reds are very largely used in the manufacture of 
signal red paints and enamels, and post-office reds. They are brilliant in hue and 
fairly permanent, but have a tendency to bleed. They are moderately fast to lime 
and spirit. At the present time they are gradually being replaced by the newer 
and more permanent reds, such as Helio Fast red, Lithol red, ete. 

This dye-stuff is on the market as Para toner, Autol red B L (Badische), Pigment 
red B (Meister Lucius & Bruning), and so on. 


Bordeaux Lake 
(Alpha Naphthylamine Lake.) 


This deep red or claret shade lake is made in the same way and by the same 
reaction as the Para red, but in this case the Para nitraniline is replaced by alpha- 
naphthylamine. 

Properties—A deep bluish claret-coloured lake, with a deep blue undertone, 
fairly permanent to light and lime. 

We will now consider the preparation and properties of one of the most 
valuable and permanent reds on the market as far as the lake manufacture is 
concerned, viz. :— 


LAKES AND LAKE PIGMENT COLOURS 143 


Helio Fast Red B L (Bayer) 


[Sitara Fast Red, Lithol Fast Scarlet R (Badische), Permanent Red 4 R 
(Berlin Aniline Co.), Monolite Fast Scarlet R (B.D.C.)] 


According to the method of Weiler-ter-Meer the process for the production of 
this extremely fast red is as follows :— 

(1) Naphthol Solution.—16 lbs. 14 ozs. beta naphthol, together with 12 Ibs. 9 ozs. 
soda lye are dissolved in 22 gals. of hot water. This solution is then made up to 
220 gals. by means of cold water. Add 24 lbs. 4 ozs. soda ash, dissolved in 22 gals. 
of water. 

The temperature of these solutions should be about 60°-70° F. 

(2) Diazo Solution.—102 lbs. 9 ozs. pure hydrochloric acid 32° Tw are poured 
into 11 gals. boiling water. ‘To this add carefully 16? Ibs. meta nitro Para toluidine, 
whilst stirring briskly at a temperature not below 210° F., so that solution takes 
place at once. 

The meta nitro Para toluidine should be run in within 3 to 5 minutes. The total 
volume of the perfectly clear solution should amount to 23-24 gals. This solution 
is then (whilst well stirring) poured slowly into 44 gals. of water and 178 lbs. 10 ozs. 
ice. Finally, whilst briskly stirring add all at once 7 lbs. 15 ozs. nitrite (97 per cent.) 
dissolved in about 24 gals. of water. The diazo solution should be perfectly clear in 
about ten minutes. The temperature during the process should be 46°-50° F. 


Helio Fast Red Lakes 


The dye-stuff is supplied in the form of 25 per cent. paste and in powder in those 
cases where the lake manufacturer prefers not to make up the dye from the 
intermediates. 

To produce the lake, all that is necessary is to add from 5 per cent. to 10 per 
cent. of the dried dye-stuff to blanc-fixe, Paris white, or other suitable base, and run 
for half an hour under the edge runners ; or alternatively add the 25 per cent. to the 
base pulped in hot water; stir well; filter press; dry; runner under the edge 
runners and sieve. 

Properties.—The resultant lake is of a yellowish red tone (scarlet) and of an 
excellent degree of fastness to light and lime, far superior to Lithol red R or Lake 
red P. Hence they are largely used in the manufacture of permanent red paints 
and enamels, distempers, etc. 

They will withstand a temperature of 150° F. without change of colour, and 
consequently are excellent for stoving reds. 


Lithol Red R (Badische), Monolite Red R (B.D.C.) 


Lithol red R is one of the most widely used and important dye-stuffs in the 
lake industry. It comes into the market in the form of a 20 per cent. or 25 per 
cent. paste as the sodium salt. 

Constitution.—2-naphthalymine-sulpho acid+B-naphthol. 


144 THE CHEMISTRY OF PAINTS 
Inthol Red Lake 


This lake is made as follows :— 


Blanc-fixe or barytes_ . : : : . 100 lbs. 
25 per cent. lithol red R paste : : AOE. 
1:10 barium chloride . : : - ae LA) 


9 


The base is mixed with ten times its weight of water, and the paste dye-stuff washed 
in through a sieve with water. The stirrers are set going and steam passed in. A 
10 per cent. solution of barium chloride is then gradually run in until complete 
precipitation is effected. The lake is just brought to the boil so that it froths up 
well, then the steam is shut off. 

The lake is well washed to remove all soluble salts, filter pressed, and dried. 
The dried lake is runnered for fifteen minutes to develop the shade. 

If the barium chloride is replaced with calcium chloride a much bluer shade is 
produced. 

According to the Badische Patent D.R.P. 175630, a lake may be made as 
follows :— 


Barytes  . f ; . 100 lbs. 

Lithol red R Pete (25 bee on, Wy: ‘ yA 

Barium chloride or calcium chloride Peri 
solution in water) . : : : : 24 5 


The paste dye-stuff is mixed with the barytes and runnered, gradually sprinkling 
in the saturated solution of barium chloride. The paste is dried, then runnered 
again to develop the shade. The author has tested this method out, and has found 
it to give excellent results. 

Properties of the Lithol Lakes—The barium lake is of a bluish-red shade, with 
a deep blue red undertone ; as calcium lake a still bluer shade is obtained. 

The lakes are of fair fastness to light, much superior to the old Ponceau lakes, 
but not so fast as the Helio Fast Reds. They are fast to water and lime, and are not 
soluble in spirit or oil (non-bleeding). They possess excellent covering power, and 
are of good stability to heat. 


CRIMson AND Ciaret LaKkes 
Lake Bordeaux B Paste (Meister Lucius & Bruning) 


Constitution. Naphthylamine-sulpho acid+B-oxynaphthoic acid. 

Properties.—These lakes are prepared according to the method used for Lithol 
red R, using calcium chloride, and give a rich crimson or claret colour of good 
fastness to ight and lime. 

The range of this class of dye-stuffs is so large that it is impossible, within the 
scope of this work, to give a fuller account of the varieties placed on the market under 
such names as Pigment Red 2 B, 4 B, 6 B (Berlin), Lithol Rubine 3 B, G (B.A.S.F.), 


LAKES AND LAKE PIGMENT COLOURS 145 


Lake Red D (M), Helio Purpurine 3 B L, Lake Red P (Meister), etc. For fuller 
description the reader should refer to special works dealing with the synthetic coal 
tar industry (see Bibliography). 


E. Morpant or ADJECTIVE DyYkE-STUFFS 


The chief representative of this important group of colours is alizarine red, 
which, owing to its exceeding fastness to light, is very largely used in the 
manufacture of permanent lake reds. Besides alizarine red there is also alizarine 
blue, alizarine heliotrope, alizarine delphinol, alizarine brown, alizarine orange, etc., 
which are used to a lesser extent by the lake manufacturer. 

Alizarine (the colouring matter of the madder root) was first prepared artificially 
by Perkin, and Graebe & Liebermann, in 1868, and is now manufactured in enormous 
quantities from anthracene by a modification of their original process. 

The constitution of alizarine is— 


CO OH a 
og. Sire 


\co% °* Non B 


Alizarine Lakes 
The dye-stufi comes on to the market in the form of 20 per cent. red paste, 
and the following example will illustrate how this lake is produced on the large 
scale :— 


Example 
Alizarine 1 B * z : ; : 20 Lbs. 
Phosphate of soda 1 : 20 ‘ : : ped it 
Soda ash 1:10 2 : : a Ea 
Turkey red oil bel0 ; ‘ ? oa ted Ur 
Alum 1:20 ‘ d . Ls ne 
Lime 1:30 


Method.—Mix the alizarine paste with 25 times its weight of hot water; add 
the weak soda phosphate solution (20 per cent.), then the solution of soda ash, 
stirring continuously. The alizarine becomes dissolved; then add the Turkey red 
oil solution previously neutralised with ammonia. 

Next gradually run in the weak alum solution, and continue stirring during the 
remainder of the process. 

Frothing takes place at this stage owing to the evolution of carbon dioxide. 
Finally add the freshly slaked lime solution, care being taken to run through a fine 
sieve to remove any grit that may be present. 

Steam is now passed in and the whole raised to the boil and boiled for three hours 
till the colour is fully developed. It is important to see that there is no iron in the 
chemicals used or in any part of the vat which comes in contact with the lake, as 
the beauty of the alizarine lake would be thereby destroyed. Wash well, filter 
press, and dry. 


146 THE CHEMISTRY OF PAINTS 


To reduce this lake 120 lbs. of blanc-fixe paste may be added. 

In the author’s opinion the finest shades of alizarine lakes are obtained by 
steaming under pressure, using rather more neutral Turkey red oil than given in the 
above formula. 

Properties.—The alizarine lakes are of the utmost value in the paint enamel 
and printing-ink trades on account of the brilliance and beauty of their shades and 
their great permanency. 

Their shades are of a rich deep bluish colour, which are quite fast to lime and 
are unaffected by oil or spirit. 


F. Lakes rrom InsotusteE Pigment DyY2&-STUuFFS 


In this class are included the more recently introduced insoluble dye-stuffs 
which have been put on the market by the various German dye factories. They 
are especially remarkable on account of their fastness, and as they are quite 
insoluble in water their method of formation into lakes or pigment colours simply 
consists In mixing up the paste with the base and drying out. Or, in the case of the 
dry dye-stuffs in adding the colour to the base under the edge runner. 

As an example of this class of dye-stuffs we may mention—Bayer, Hansa 
Yellow 5 G, Helio Chrome Yellow 28227, Helio Chrome Yellow G L, Helio Fast 
Yellow 6 GL, Helio Fast Pink R L, Algole Blue 3 R, Helio Orange C A G, Pigment 
Chlorine G G, Thio Indigo, etc. The undermentioned examples will illustrate 
the preparation of lakes from these pigment dye-stuffs :— 


Example 1. Example 2. 
Barytes. : . 120 lbs. Blane-fixe . ; . 100 lbs. 
Zinc oxide . ; a OU yr Hansa yellow paste . 50 ,, 
Helio Fast Pnak RL. cee 

Example 3. Example 4. 
Barytes : ee DU LDH: Barytes  . : ~) pO ae 
Orange lead : es ae Permanent red 4 Rextra 15 ,, 
Helio OrangeCAG . Rage Zinc oxide . : ~ De Bb ae 


Every year new insoluble dye-stuffs are being put on the market, and it is only 
a question of time when the lake manufacturer will have a range of dye-stufis at 
his disposal equal in fastness to the inorganic colours, and be able to dispel the 
erroneous idea still held by many that all dye-stuff colours are necessarily fugitive. 


SCHEME FOR THE ANALYSIS OF LAKE PIGMENTS 


The analysis of lakes and lake pigments may be conveniently divided in the 
following manner :— 

1. The analysis of the base or “ carrier.” 

2. The identification of the dye-stufl—or several dye-stufis, as the case may be 
—which have been used in their production. 


LAKES AND LAKE PIGMENT COLOURS 147 


The analysis of the base or carrier is a comparatively simple matter, as the 
number of inert materials used for this purpose is limited, and the usual methods 
of inorganic analysis will readily identify them. 

The identification, on the other hand, of the dye-stuff or dye-stuffs that have 
been used in the production of a lake is one that presents very great difficulties, 
not only on account of the large number of dye-stuffs that are now employed, but 
also because the process used in the precipitation of several dye-stufis on one base 
(such as in the preparation of combined or “ mixed” lakes) tends to mask the 
reactions, and thus prevent their ready determination. 

We will now briefly indicate the methods in use for the analysis of lakes and 
lake pigments. 

Physical Tests 


A preliminary examination of a lake as regards its physical characteristics 
will often give valuable indications as to its composition, and should always be 
carried out. 

If, for example, a small portion of the lake be rubbed up on a white palette 
in oil, its texture will indicate generally the nature of its base, and will serve to 
identify it. | 

Alumina bases, for instance, yield tough transparent lakes, which are hard to 
grind out, while blanc-fixé bases, on the other hand, are extremely soft in texture, 
and have moderate body and covering power. Barytes bases are readily identified 
by their peculiar, harsh, gritty texture, however fine the barytes used may be. 

The colour of the lake in oil, and its undertone, should be carefully noted, as 
this often gives a clue by means of which the dye-stuff precipitated on the base may 
be readily ascertained. For example, Lithol lakes give in oil deep blue undertones, 
while Para reds give slight brown or colourless undertones. 


Analysis of the Base or Carrier 


Take 2 gms. of the lake, and gently ignite in a crucible till all the dye-stufis are 
burnt off. The residue left is generally white. Weigh the residue. Treat it with 
boiling hydrochloric acid; filter and wash well. Test residue for barytes by the 
flame test. 

The filtrate is tested for alumina, zinc oxide, and so on, and, if required, the 
amounts present may be estimated in the usual manner. 

The bases in most common use are barytes, blanc-fixe, alumina, alumina blanc- 
fixe, green earth, whiting and terra alba. Red and orange lead, zinc oxide, and 
white lead are also used in addition to give body to a lake, and also to tone up the 
colour. 

The Identification of the Dye-stuffs 

The identification of the dye-stufis in a lake is a very tedious operation, except 
in those cases where the lake contains only one simple dye-stufl, which gives 
characteristic tests by which it may be readily recognised, such as the eosines, 
alizarines, and so on. 


THE CHEMISTRY OF PAINTS 


148 


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SHUVT ANITINY LINVLYOdW]T HXYOW AHL AO AWOS NO SINANVAIY SHOTaVA AO NOILOVAY AH, 





LAKES AND LAKE PIGMENT COLOURS 149 


The usual method of procedure is to treat the lake with various reagents, and 
note its behaviour under such treatment. This is carried out in the following way :— 

A portion of the lake is boiled up in a test tube with (1) water, (2) alcohol, 
(3) alcoholic potash, (4) freshly distilled aniline, (5) sulphuric acid, (6) hydrochloric 
acid, (7) stannous chloride solution-+-hydrochloric acid, (8) acetic acid. 

The colour of the dye-stuff obtained on filtration is carefully noted. 

The table on page 148 gives the reactions obtained with some of the lakes which 
are In common use in the paint and printing-ink trades. (For a more detailed 
account the reader is referred to special works dealing with the subject, such as 
Schultz and Julius, “A Systematic Survey of the Organic Colouring Matters,” or 
George Zerr, “ Bestimmung von Teerfarbstoffen in Farblacken.’’) 

The identification of the dye-stuffs present in a given lake by means of the 
reagents given above is very much facilitated by repeating the tests on known 
standards. For this purpose standards are previously prepared of all the dye-stufis 
which are in common use in the manufacture of lakes by precipitating 5 and 10 per 
cent. respectively of the dye-stuff on to (1) an alumina, (2) blanc-fixé, and (3) barytes 
base. By this means is obtained a large range of lakes containing a definite and 
known percentage of given dye-stufis on which tests with different reagents can be 
carried out. 

Thus, for example, if a given lake is identified as being a Lithol red on blanc- 
fixe, then the tests can be repeated on the 5 and 10 per cent. Lithol red lake standards 
previously prepared, and so checked. In addition to this the strength of the lake can 
also be determined by a comparative strength test against these standards. 

If the above tests be carefully and systematically carried out, it will be possible, 
after some experience, to identify not only the dye-stuffs present in any body, but, 
also the amount, and by this means to make up similar lakes having identical 
properties and shades. 

The following coal tar colouring matters, manufactured by the British Dye- 
stuff Corporation (1922), are specially suitable for the manufacture of lake colours. 

All the dye-stufis mentioned are readily soluble in water, except— 


Monolite Red R = Badische Lithol Red 
© . Fast Searlei: i. = a Fast Scarlet R 
y Red P = 7 Lake Red P 


The table appended shows the fastness of these lakes as regards light, spirit 
and water :— 














150 THE CHEMISTRY OF PAINTS 
SOLUBLE COLOURS 
Fastness to 
No. 
Light Water. Spirit 
1 | ChrysophenineG . Good Insoluble Soluble 
2 | Naphthol Yellow F Y Very good Slightly soluble | Insoluble 
3 | Acid Yellow 85539 Very good Insoluble Insoluble 
4 | Citronine Y Concentrated . Fair—good Slightly soluble | Soluble 
5 | Metanil Yellow Y . Poor—fair Slightly soluble | Soluble 
6 | Metanil Yellow WM Poor Slightly soluble | Soluble 
7 | Acid Orange G Poor Insoluble Soluble 
8 | Coomassie Milling Scarlet G Poor Insoluble Slightly soluble 
9 | Acid Scarlet R : Poor Insoluble Slightly soluble 
10 | Ponceau RG . Poor Insoluble Slightly soluble 
11 | Scarlet 81024 . Poor Insoluble Insoluble 
12 | Acid Scarlet 3 R Poor Insoluble Slightly soluble 
13 | Milling Scarlet 5 B Poor Insoluble Soluble 
14 | EKosine YS. Poor Slightly soluble | Soluble 
15 | Lake Scarlet 3B. : Very good Insoluble Insoluble 
16 | Chlorazol Fast Pnk BK . Very good Insoluble Insoluble 
17 | Azo Geranine B ‘ Fair Insoluble Insoluble 
18 | Pure Bordeaux B. Poor Soluble Soluble 
19 | Fast Acid Blue R H Good Insoluble Insoluble 
20 | Coomassie Violet R . Poor Insoluble Soluble 
21 | Soluble Blue 3 M Fair Insoluble Soluble [extent 
22 | Pure Soluble Blue Fair Insoluble Soluble to some 
23 | Alkali Blue 4 B Fair Insoluble Soluble 
24 | Indulme5B . Good Insoluble Soluble 
25 | Durasol Acid Blue B Very good Insoluble Insoluble 
26 | Disulphine Blue A Poor Insoluble Slightly soluble 
27 | Acid Green G . Poor Insoluble Soluble 
28 | Naphthol Green B 9211 Ke Excellent Insoluble Insoluble 
29 | Nigrosine G Crystals Good Insoluble Soluble 
30 | Chlorazol Black F F X Good Insoluble Soluble 
31 | AuramineO . : Poor Soluble Soluble 
32 | Chrysoidine Y R P Fair Soluble Soluble 
33 | Bismarck Brown G . Fair Soluble Soluble 
34 | Bismarck Brown R 100’s Fair Slightly soluble | Soluble 
35 | Safranine T. Concentrated. Poor Soluble Soluble 
36 | Tannin Pink C : Poor Soluble Soluble 
37 | Magenta Large Crystals Poor Soluble Soluble 
38 | Magenta 2 B Powder Poor Soluble Soluble 
39 | Methyl Violet 2 B Conc. Poor Soluble Soluble 
40 | Methyl Violet 10 BL Poor Soluble Soluble 
41 | Indine Blue 2R D Very good Soluble Soluble 
42 | Methylene BlueGS. Very good Soluble Soluble 
43 | Turquoise BlueG . Poor Soluble Soluble 
44 | Malachite Green Crystals A Con- 
centrated . Poor Soluble Soluble 
45 | Brilliant Green Crystals y Poor Soluble Soluble 
INSOLUBLE COLOURS 
Fastness to 
No. 
Light Water Spirit 
46 | Monolite Fast Scarlet R paste Excellent Insoluble Insoluble 
47 | Monolite Red P paste Very good Insoluble Soluble 
48 | Monolite Red R paste Fair Insoluble Soluble 


CHAPTER XIV 


THE ANALYSIS AND EVALUATION OF PIGMENTS 
ACCORDING TO THEIR PHYSICAL PROPERTIES 


Tue chemical analysis of the various pigments has already been indicated under 
their respective headings in the previous chapters dealing with their manufacture 
and properties. 

It is desirable, however, to give also a brief account of the general physical 
tests which should be applied to pigments in order to determine their suitability 
and properties when used in the manufacture of paints. 

- The chief physical properties of pigments which should be considered in this 
connection may be briefly enumerated as follows :— 


. Specific gravity. 

. Fineness. 

. Colour, brightness and cleanness of tone. 
. Oil absorption. 

. Strength. 

Hiding power. 

. Covering power. 

. Permanency. 


DNATRWNDe 


1. SPEcIFIc GRAVITY 


The specific gravity of a pigment may be determined by 
any of the well-known physical methods. The specific gravity 
bottle is especially suitable for the purpose, and the deter- 
mination is carried out in the following manner :— 

A 50 gm. bottle (Fig. 21) is weighed. The weight of 
distilled water at 15-5 C. which the bottle contains is meg OE enue, 
ascertained. The pigment is now introduced into the dry Ghavere Bora: 
bottle, the whole is weighed, and the weight of the pigment 
is obtained by difference. 

The bottle containing the solid is now filled with distilled water; air bubbles 
enclosed in the pigment are removed by heating or shaking; the liquid is 
brought to the temperature of 15-5° C.; additional water is added if necessary 
to fill the bottle quite full; then the stopper is inserted and the excess water 

1 151 





152 THE CHEMISTRY OF PAINTS 


oozing out is carefully wiped away, and the bottle and its contents are weighed 
again. 

The ratio of the weight of the pigment to the weight of water displaced by it 
is the specific gravity of the pigment. 


Average Specific Gravity of some of the Common Pigments 


Basic carbonate white lead . 6-81 Litharge . : : ees 0 \ 
Basic sulphate white lead . 6-41 Purple oxide ; ; . 5384 
Normal lead sulphate . . 6.08 J.F.L.S. yellow ochre . - 299 
Zinc oxide . : : . 5-66 Raw sienna . : : . 532 
Lithopone . : : . 4°30 Raw umber. : ; . 4-52 
Barytes j : . 4:46 Pale chrome yellow. . bro 
Blanc-fixe . : 3 . 4-28 Pale chrome green , . 813 
Terra alba . ; : . 2:34 Zinc chrome ; : . 9°69 
Paris white . : ; » #261 Prussian blue. : Pa iY | 
Precipitated chalk : . 2-56 Ultramarine blue . : - 260 
China clay . ; 4 . 2-65 Vegetable black . : Re 
Asbestine . : : ee Graphite . ; ; . 2°46 
Silica . . ; , . 2:60 Bone black . : : . 2935 
Red lead. : F . 8-68 Venetian red : : ~ 5-28 
Titanium white . ; . 4-00 Vermilion . ; : . 6°83 
2. FINENESS 


The testing of a pigment as regards its fineness is of the utmost importance for 
many reasons. In the first place a certain degree of fineness is obviously necessary 
before the mixture of solid substances and oil can be uniformly spread over a surface 
with a brush, as very coarse particles will naturally settle out quickly from the oil. 
Paints made up from coarse pigments will dry off with a rough and displeasing 
surface or finish. 

Further, the fact must not be lost sight of that the hiding power of a pigment 
is inversely proportional to the diameter of the particles, or, in other words, the 
smaller the particles the greater the hiding power. 

In addition, the finer the particles of a given pigment, when mixed to a painting 
consistency in a given medium, the greater the covering or spreading power of that 
pigment. 

The rough and ready test which is usually applied to a pigment to determine 
its fineness is carried out in the following way :— 

A small portion of the pigment is spread on a white porcelain palette and 
rubbed with a palette knife—(1) in the dry state, (2) with oil, (3) with turpentine. 
By this means a general idea will be obtained as to its texture and degree of 
fineness as compared with a standard sample of known fineness. 

The comparative fineness of a pigment may also be ascertained by noting the 
time required for 5 gms. of the pigment, when shaken up in a cylinder filled with 





ANALYSIS OF PIGMENTS 153 


petroleum ether (or other liquid of low specific gravity) to settle out as contrasted 
with other pigments of the same type. 

The quantitative estimation of the amount of coarse particles in a pigment 
may be determined by sieving the material through a series of fine sieves and silk 
bolting cloths, and weighing the various residues, or by means of the Elutriator 
(see Chapter VI.). 

The best means for separating and estimating pigments according to size is by 
the Thompson Classifier, a description of which is given in the “ Proceedings of the 
American Society for Testing Materials,” vol. x., 1910. 


3. CoLouR 


A coloured object, not self-luminous, owes its colour to the fact that it absorbs 
some colours of the light which falls on it, reflecting and scattering the rest. Thus 
blue paint absorbs red and 


yellow, reflecting only green, 
blue and violet. Yellow 
paint absorbs all but red, 
yellow and green. Hence 
when blue and yellow paints 
are mixed, the only colour 
which is notabsorbed is green, 
- which is reflected both by the 
blue and the yellow pigments. 


Standard 
Glasses 







Yi 


WZ2ZZIA 


ODIM OES. 








7) 


SS 







SSSSs5 









Ny 
Ny 
N 
N 
hy 

Las 
N 
N 
N 
NY 
N 
Ny 
AY 
Ny 
Ny 
\ 
My 
N 
Ny 

x 
NY 
LY 
N 
RY 
S 
A) 
N 
Ny 
\ 
Ny 
\ 
N 
Ny) 
8 
N 
s) 
N 
Ny 
\ 
Ny 
& 
Ny 
N) 
S 
N) 
N) 
\ 
N 
\ 
N) 
‘ 
N 
& 
N 
x 


. 
SELLILLLLL, N 







SSSSS55 


SS 
NZ 






Pigment 


Fie. 22.—Tar Lovisonp TINTOMETER. 


The colour of a given 
pigment is always ascertained by comparison with other standard colours of a 
similar type. 

Thus the purity of the colour of a white pigment is determined by comparison 
with other white pigments, both in their dry state and when ground in a colourless 
medium such as bleached poppy seed oil. 

The colour may be described as being a dirty white, or of a bluish shade, yellowish 
tone, greyish tint or tone, and so on, according to the colour tone which it possesses. 

Coloured pigments are likewise classified by comparison with other pigments of 
a similar shade, and careful note should be taken of their brightness and cleanness 
of shade, depth of colour, and of their undertone and overtone. 

For example, two Prussian blues compared side by side may show considerable 
differences ; one may be of a bright clean tone, with a violet shade and bronzy 
lustre, while the other may be of a dirty greenish shade and devoid of any bronzy 
appearance. 


The Tintometer 


Attempts have been made to construct an instrument by means of which records 
of colours may be accurately registered. The Lovibond Tintometer (Fig. 22) is by 
far the best instrument of this class, and by its use it is possible to determine the 
colour and tint of all materials used in decorative work. 


154 THE CHEMISTRY OF PAINTS 


The instrument consists of a double tube ending in an eyepiece at the smaller 
end. At the other end are equal apertures for viewing the colour to be measured 
alongside of standard glasses. 

To apply the instrument for colour measurements there is provided a set of 
standard coloured glasses, which can be placed in suitable grooves at one side of the 
wider end of the double tube, while on the other side is put the colour which is to 
be measured. 

One or more of the standard colour glasses are put into the tube until the colour 
and tint of the pigment is exactly matched. A note of the numbers of the glasses 
thus records the matched colour. | 

Over 400 standard coloured glasses are supplied, coloured in various degrees of 
intensity and in even gradations. 


4, Or, ABSORPTION 

The oil absorption or oil-carrying capacity of a pigment is, for practical purposes, 
the amount of oil required to grind a pigment into a stiff paste. As is well known, 
the greater the pressure the less the amount of oil required to convert the pigment 
into paste form. The oil absorption of a pigment as compared with that of other 
pigments is usually determimed approximately as follows :—5 gms. of the pigments 
are weighed out on to a palette, and linseed oil is added drop by drop until 
the pigments when rubbed up hard under the palette knife are converted into 
a stiff paste. 

The number of c.c. of oil required is noted and the result expressed as the 
number of gms. of oil required to grind 100 gms. of pigment into a stiff paste 
form. The oil absorption test is of considerable value in the manufacture of colours 
ground in oil which are sold by weight, as usually the cost of the oil is a good deal 
greater than that of the pigment. 

Thus, for example, in the case of two ochres of similar colour, tone, etc., it is 
obviously more economical to select the one that requires the lesser amount of oil 
to convert it into paste form. As a general rule the heavier the pigment the less 
oil it absorbs. 


Approximate Oil Absorption of Various Pigments 
Linseed Oil (by weight). 


White lead (Dutch process) . ‘ } . tT. percent. 
White lead (chamber process) ae See Fe 
Zinc oxide : : : : ‘ oot - 
Lithopone . : . : 3 : ema a 
Barytes . : : : : ; Meee Cite Te 
Whiting . : : ; : : . 22 “A 
J.F.L.S. ochre . : : : : rar, “ 
Turkey umber . : : ; : >. 40 93 
Vandyke brown . : 2 ; ; Rey ks, FP 


Vegetable black . : : ; . . 90 F 





ANALYSIS OF PIGMENTS 155 
Linseed Oil (by weight). 


Lemon chrome . : ‘ é : 14 per cent. 
Ultramarine blue ; 7 \ : 1b ee 
Prussian blue. , : ; ; On ies 
Brunswick green . : : ‘ AG ese 
Titanium oxide . : : ; : SP Talk ae aie 


5. STRENGTH 


The strength test of a pigment is of the utmost importance in its valuation. 
The pigments should always be compared with carefully selected standards of a 
similar type in the following manner :— 


White Pigments—Zine Oxide, White Lead, Inthopone, etc. 


Weigh out carefully 1 gm. of the white pigment under test on to a white 
porcelain palette, and add 0-1 gm. of standard Prussian blue. Then add sufficient 
bleached linseed oil drop by drop from a dropping 
bottle till the pigments on thorough grinding are 
converted into a stiff paste form, and the blue is 
intimately mixed with the white pigment. Note 
the number of drops of oil used. Repeat in 


ne 


es et ee ee a ee 


1 
1 
{ 
t 
| 
! 
! 
1 


precisely the same manner with a standard sample Sistdard Sample 
of zine oxide, or, if preferred, with a standard 

; ais Fic. 23.—Microscorps SLIDE WITH 
white of the same composition as the one under Buaweeton Tuer: 


examination. Transfer the tints thus prepared to 
a microscope slide (Fig. 23), and spread out evenly side by side till they are just 
touching one another. 

Compare the tints thus obtained on both sides of the glass. 

If the standard be bluer than the sample under test then obviously it is weaker 
than the sample, and vice versa. 

Sometimes standard ultramarine blue is used in place of Prussian blue in the 
proportions of white 20 parts to ultramarine blue 5 parts. 


Red Colours—Red Oxides, Aniline Reds, etc. 


Use 0-1 gm. of the sample to 1 gm. of standard zinc oxide, or 0-25 of colour to 
1 gm. of standard white lead. 


Greens, Blues and Blacks 
Take 0-01 gm. of the sample to 2 gms. of standard zinc oxide. 


Chromes (all except Orange) 


Take 1 gm. of the sample to 0-25 gms. of standard Brunswick blue (10 per cent. 
Prussian blue on barytes). 


156 THE CHEMISTRY OF PAINTS 


Orange Chrome 
Take 0-1 gm. of the sample to 1 gm. of standard zinc oxide. 


6. Hipinc PowER 


The hiding or obscuring power (often called body) of a pigment when made 
into paint form is the property it possesses of obliterating or masking the surface 
over which it is spread. This varies inversely as the diameter of the particles, or, 
to put it in other words, the smaller the particles the greater the obscuring power. 

In the case of a white pigment the obscuring power is the function of its capacity 
for reflecting light. The amount of reflected light depends closely upon the number 
of reflections from a pigment film of a given thickness and on the size of the particles 
in the pigment film. 

The hiding power of a pigment must not be confused with its covering power. 
Thus while two coats of white lead paint are about equal in opacity or hiding power 
to three coats of zinc oxide, the covering power of the latter is, as is well known, 
considerably greater than white lead. 

Lakes prepared by precipitating dye-stuffs on an alumina base are known as 
transparent colours, and although they may cover well, they are deficient as 
regards body. 

The determination of the hiding power of pigments is usually carried out in the 
following manner :—A white board traversed with black lines is carefully divided 
into equal areas. The pigments to be tested for opacity or body are ground up in 
raw linseed oil to a stiff paste form, careful note being taken of the amount of oil 
used. A weighed-out quantity of these stiff pastes is thinned down to brush 
consistency with a standard paint medium consisting of 10 parts of pale boiled oil, 
2 parts of turpentine, and 1 part of pale terebine. 

The prepared paints are weighed out into tins each provided with a small brush. 
The paints are then brushed on to the equal divisions of the board as thinly and 
evenly as possible, a sufficient number of coats being applied till the black is 
completely obliterated in each case. As a rule two coats will suffice, except where 
the body of the paint is very poor, when more coats will be necessary. 

Each tin with brush is then weighed after this operation in order to ascertain 
the weight used. It is then easy to calculate the relative opacities of the pigments 
under test. 

A large number of tests should be made so as to get a fair average result and 
to reduce the error caused by the laying on of any excess of paint over the minimum 
required to produce complete obliteration. 


Spray Test 
The author has obtained exceedingly good relative results by breaking the 
paints down to spraying consistency and spraying them on to a given area of doped 
fabric—the weight of which is known—until complete obliteration has taken place. 
The fabric is again weighed after the paint has dried on. 





ANALYSIS OF PIGMENTS 157 


This process was found to give much more uniform results than could be 
obtained by the brush method, due doubtless to the elimination of the personal 
error. Moreover, much thinner and more uniform coats of paint can be applied by 
spraying than is possible by the brush method. 

Dr Pfund has invented a very simple instrument called the “ cryptometer ” 4 
for determining the true numerical values of the obscuring powers of pigments 
and paints. 


7. CoveRiInG Power 


The covering or spreading power of a pigment is measured by the greatest area 
over which unit mass of a pigment mixed to a painting consistency with a given 
medium can be uniformly spread with a brush. 

As a rule two pigments in an equally fine state of subdivision will show 
spreading powers inversely proportional to their specific gravities. 

The covering power of pigments is usually determined by the relative areas 
covered by 100 gms. of the pigments when reduced to paint consistency. The 
following method is usually adopted for determining the covering power of 
pigments :— 

The pigments are made up into paint form as described in paragraph 6 and 
brushed on to primed boards, care being taken to spread the paints as thinly and 
uniformly as possible. 

The area covered by a known weight of the paint is then measured and the 
result expressed either as the number of square feet covered by 100 lbs. of the 
pigment, or more usually the number of square feet covered by 1 gallon of the paint. 

The following table gives some of the physical data obtained by practical tests 
on zinc oxide, white lead and lithopone :— 


Zine Oxide. White Lead. Inthopone. 
(30 per cent.) 


Specific gravity . ? : 5-66 6-81 4-30 
Oilabsorption . , : 20 8 15 
Relative strength : : 100 57 70 
Relative hiding power . : 100 156 120 


Relative covering power ; 100 62 69 


8. PERMANENCY 


In addition to the various physical properties of pigments which have already 
been discussed, there are others which require to be carefully considered in estimating 
the value of a pigment as a paint material, chief of which are durability and colour, 
stability on exposure to sunlight, and weathering influences. 

The simplest method of testing the permanency of a pigment is to make it up 
into paint form and brush one or two coats on to wood and iron and expose to the 
atmosphere. 

A portion of the painted surface is covered with a strip of wood to protect it 


1 Farben Zeitung, Jan. 1920. 


158 THE CHEMISTRY OF PAINTS 


so that comparisons can be made later on between the exposed and protected 
surfaces. 

The paint should be washed down from time to time, and the results of the 
weathering influences noted as regards (1) change of colour, (2) cracking, and 
(3) chalking. In this way an estimate may be formed as to its durability and colour 
stability as compared with the portion protected from exposure. 

The permanency of pigments to light may also be tested by grinding them up 
in gum arabic solution and painting them on to a piece of non-absorbent paper 
in strips side by side. The paper is hung up inside against a window exposed to as 
much sunlight as possible, care being taken to protect a portion of the painted paper 
from the light by means of a strip of black paper which may easily be removed 
from time to time so that a comparison may be made as to the effect of the light 
on the various colours. 

A quick test for determining the colour stability of pigments may be made by 
exposing paint films on glass to the rays from the mercury lamp. 

The results of exposure tests on the commonly used white pigments that are 
made up into paints indicate that white lead, while it has the defect of tending 
to turn slightly brown, especially on exposure to town atmospheres, possesses 
remarkable properties as regards durability and stability under the most severe 
weathering conditions, and is far superior in its protective qualities to any other 
white pigment in common use. 

Zinc oxide, titanium oxide, and antimony oxide retain their colour extremely 
well for a time, but after exposure for a period over twelve to eighteen months they 
tend to show chalking effects. 

Lithopone ! paints, on the other hand, readily discolour, turning grey, and after 
a few months’ exposure commence to chalk and shell off; hence they are of little 
value as protective paints for outdoor use. 

The natural earth colours such as the ochres, umbers, red oxides, etc., are 
extraordinarily permanent, and retain their colour even after long exposure to the 
most severe conditions. 

Brunswick greens, chromes, Prussian blues, and other similar manufactured 
colours are as a rule moderately permanent. Ultramarine blue and vermilion 
are, however, very permanent colours. 

Aniline lakes show remarkable differences as regards their colour stability, 
e.g. alizarine, helio fast rubine R L, helio chrome yellow G L, lakes, etc., exhibit 
striking permanency to light, while other lakes, such as those made from eosine, 
magenta, methyl violet, etc., are very fugitive, and lose their colour completely 
after only a few weeks’ exposure. 

The permanency of a colour when exposed to sulphuretted hydrogen and 
acid fumes should also be considered ; their stability or fastness to lime and alkalies 
is also of great importance when intended for use in the manufacture of distempers 
and calsomines (Lime Fast Colours, see Chapter XIII.). 

The action of pigments on one another, and on the oil or varnish medium in 


1 Certain brands of lithopone are now manufactured which are fast to sunlight (see Chapter VI.). 


ANALYSIS OF PIGMENTS 159 


which they are ground when made up into paint form, should also be tested to 
determine whether they are inert to one another or whether there is any action 
between them. 

Some pigments, for example zinc oxide, when ground in acid varnish mediums, 
such as rosin or Congo copal varnishes, in the preparation of enamels, tend to 
“feed ” or thicken up. 

White lead, as is well known, tends to form a lead soap when ground in linseed 
oil, and to this fact may be ascribed in a large measure the remarkable elasticity 
and durability of lead paints; titanium oxide and antimony oxides, on the other 
hand, are inert pigments, and have no influence on the medium in which they are 
ground. 

Pigments containing sulphur when mixed with lead pigments are liable to cause 
discoloration, and on this account such mixtures should be avoided. 

Pigments used in the pottery trades must be capable of withstanding high 
temperatures, hence only pigments such as cobalt oxide, tin oxide, green oxide, 
chromium, ultramarine blue can be used. 

Colours that are soluble in water, e.g. calcium chromate, etc., also those that 
possess toxic properties and are unstable to light, such as emerald green, are unsuitable 
for general use as pigments in the manufacture of paints or protective coverings. 


PART III 


Varnishes, Lacquers and Japans 


CHAPTER XV 


INTRODUCTION, COLOPHONY, SOFT RESINS, BALSAMS 
AND FOSSIL GUMS 


INTRODUCTION 


VARNISHES and lacquers may be defined as solutions of various natural balsams, 
resins, lacs or fossil gums dissolved in suitable solvents or diluents, with or without 
the addition of a drying oil such as linseed oil. 

They dry, as a rule, when applied in thin films with a hard, tough, lustrous 
surface or “ face.” 

They are applied to various objects with a view to giving them a pleasing, 
finished appearance; at the same time they have a utilitarian aim in that they 
serve to protect the material to which they are applied from external injury. 

The art of lacquering has been known to the Chinese, Japanese, and other 
Asiatic races from a very remote period. 

The manufacture of oil varnish from linseed oil and gums is of more recent 
origin ; the earliest record we have of it is from a monk named Theophilus, who 
published directions for making linseed oil varnish in the twelfth century. 

Lacquers and varnishes may be classified under the following two groups :— 

(1) Oil varnishes. 

(2) Spirit varnishes or lacquers. 

Oil varnishes dry through the evaporation of the solvent and the subsequent 
oxidation of the sticky gum oil residue into hard films, through the absorption of 
oxygen from the air. 

In the case of spirit varnishes the drying action is simply due to the evapora- 
tion of the solvent, which leaves a solid residue behind. 


RAW MATERIALS 
The raw materials used in the manufacture of varnishes and lacquers are 
mainly as follows :— 
1. Colophony (rosin), balsams, soft resins, shellacs and fossil gums; also 
celluloid, nitro-cellulose, cellulose acetate and synthetic resins. 
160 


DESCRIPTION OF RESINS 161 


2. Drying oils, such as linseed oil and wood oil. 

3. Solvents and diluents, such as turpentine, alcohol, and other volatile liquids. 

4. Dryers, siccatives and terebines. 

The various resins used in the manufacture of varnishes will be now briefly 
described as regards their origin and sources of supply, as well as their chief 
properties. 

For convenience the resins will be classified in two groups :— 

1. The soft resins, including the balsams and colophony or rosin, which is by 
far and away the most important and largely used of all the resins. 

2. The hard resins or fossil gums, such as animi, amber, kauri, copal, and 
So on. 


(1) CotopHony (Rostn, Common Resin) 


Colophony, known commercially as rosin, which term is to be used in 
preference to resin as being less likely to be confused with other resins, in the 
residuum left after the expulsion of the oil of turpentine from the resinous exudation 
of coniferous trees (Gum Thus). 

The molten rosin is run out of the stills into casks in which it solidifies to a 
vitreous mass. 

Rosin is imported in large quantities chiefly from the United States, France 
and Spain. American rosin, which forms the bulk of our supplies, is derived mainly 
from the long leaf Pinus Australis, and French rosin from Pinus Maritima, the 
composition of the two being somewhat different. 

The colour of rosin depends on the manner in which the distillation has been 
carried out, It varies in colour from “ Extra pale” (“ W G” window glass) and 
water white (“ W W ”’) to F, G, B, G, and B grade; B grade being nearly black. 


Composition 


Rosin has been the subject of innumerable chemical investigations over many 
years, but so difficult have these researches proved that there are still many 
problems connected with the chemistry of rosin that await solution. 

Rosin consists mainly of free acids (abietic acid). Tschirch in 1903 by treating 
an alcoholic solution of American colophony with alcoholic lead acetate obtained 
three abietic acids—alpha, beta and gamma. These results were afterwards 
confirmed by Seidel. _ 

Abietic acid has the formula C,,H,,0,. 

French rosin consists mainly of pimaric acids, which are closely related to 
the abietic acids. 

Pimaric acid exists in both levo and dextro form, and both give crystalline 
ammonium salts, whereas those of abietic acid are gelatinous. 

The pimaric acids appear to have greater stability than the abietic acids of 
American colophony. 

Rosins are generally supposed to be oxidation products of the terpenes, with 
which they are associated in the natural terpenes. 


162 THE CHEMISTRY OF PAINTS 


Properties and Uses 


Colophony or rosin is a brittle solid with a glassy fracture. It has a 
characteristic odour on gently warming. It softens at about 80° C. and melts at 
110-135° C. 

Rosin is slightly heavier than water, its specific gravity being 1-067 to 1-081. 

It is soluble in alcohol, ether, turpentine, white spirit, and practically all 
organic solvents, and in oils. 

It is saponified by alkalies, which combine with the abietic acid to form the 
rosin soaps which are so largely used in the soap industry. 

When rosin is heated at temperatures above its melting point it yields gaseous 
products and a distillate of rosin spirit and rosin oil (see Chapter XVI.); but 
in a current of superheated steam (above 200° C.) it can be distilled without any 
apparent change. Rosin is extensively used in making varnish. 


The Analysis of Rosin 


An analysis of rosin is hardly ever called for as it is one of the cheapest 
resins on the market and hence is not liable to adulteration. 

It may be readily detected by the Liebermann-Storch test which is carried 
out as follows :— 

Boil 5 gms. of the material, supposed to contain rosin, with 30 c.cs. of acetic 
anhydride; cool, pipette off the acetic anhydride, and add a drop of sulphuric 
acid 1-53 specific gravity. If rosin be present, even in traces, a fugitive violet 
colour will be produced. 

The amount of rosin present—e.g. in an oil or fat—may be determined by the 
Twitchell method, which depends on the fact that when dry hydrochloric acid is 
passed through a solution in absolute alcohol no rosin esters are formed. 


Analytical Constants of Commercial Rosin 


Specific gravity at 15-5° C. ; : : .  1-065-1-082 
Melting point . ‘ : : : : SEDO SG 
Acid value : ; : 4 ; : . 164 
Saponification value . : ; ; ° 7 ore 

Todine value. ' : : é . 80-220 
Ester value. ; ; . : ; 18 
Unsaponifiable . . : : 2 , : 7 


The analytical constants given above are only approximate as the figures — 
obtained vary considerably in different varieties of rosin. The iodine value varies 
to such an extent that it is of no value as a constant for rosin. 


HARDENED Rosin 


If rosin be raised to about 200° C., and lime or zinc oxide stirred in, a vigorous 
reaction takes place owing to the combination of the rosin acids (abietic acid) 
with the lime or zinc oxides whereby a calcium or zine resinate is produced. 


DESCRIPTION OF RESINS 163 


The melting-point of the rosin is thereby raised and so these resinates which 
are known as “hardened” rosins are used very extensively in the manufacture 
of hard-drying varnishes. 

Varnish made with rosin tends to dry sticky, but with calcium or zinc resinate 
it dries off hard, and is more durable and withstands atmospheric influences better. 

Other metallic resinates such as copper, cobalt, lead, manganese, aluminium, 
and others, are also produced in a similar way to that of the calcium and the zinc 
resinates. 

Copper resinate is used in anti-fouling compositions (see Chapter III.), while 
the resinates of lead, manganese and cobalt are largely used as driers (see 


Chapter XX.). 
Rosin Esters on Rosin Gums 


A resin ester is made by combining a resin acid with an alcohol, with the 
elimination of water. Glycerine rosin esters are made by combining rosin with 
glycerol. 

The colophony is melted in large iron pans, or in autoclaves, with about 
10 per cent. of its weight of glycerol in the presence of catalytic and dehydrating 
- agents. The glycerol combines with the rosin to form a nearly neutral ester gum. 

The rosin glycerine ester gums are largely used in the manufacture of outside 
varnishes, especially in conjunction with wood oil on account of their superior 
wearing and weather-resisting properties as compared with the lime-hardened rosins. 

Varnishes made with ester gums, on account of their low acidity (A.V. 10-15), 
do not thicken or liver up with zinc oxide, a property which is of extreme importance 
in the manufacture of enamels. 

Ester gums are insoluble in alcohol, but perfectly soluble in turpentine and 
white spirit. 

. BALSAMS 
Common Frankincense (Gum Thus., Galipot, Thus. Americanum.) 


Crude turpentine, which concretes on the trunks of various coniferous trees, 
especially in France and North America, was formerly scraped off and used in 
pharmacy under the generic name of balsam. 

The ordinary fresh crude turpentine (Gum Thus.) is a soft pale yellow opaque 
viscous material (which is intermediate between spirit of turpentine and rosin) 
with a turpentine-like odour. On keeping, it becomes dry and brittle and darker 
in colour, and loses its odour. 

These natural balsams have a limited use as softening agents to lessen the 
brittleness of various varnishes and lacquers. 


CanaDA BaLsaM 
(Canada Turpentine, Terebinthina Canadensis.) 


This balsam is the oleo-resin obtained from Abies balsamea, a species of 
Canadian pine tree. 


164 THE CHEMISTRY OF PAINTS 


Properties.—It is of a pale yellow and faintly greenish transparent colour of 
the consistence of thin honey. It has a peculiar, agreeable aromatic turpentine- 
like odour, and a slightly bitter acrid taste. 

On exposure to the air it slowly dries, giving a transparent film. Its specific 
gravity is about -998. It is soluble in benzol, ether and alcohol. 


Bureunpy PitcH 
(Pix Burgundica.) 


The resinous exudation obtained from a species of pine (Pinus abies, Abies 
excelsor, Picea excels) which flourishes in the Vosges and the Alps. 

Properties.—It is hard and brittle, yet gradually takes the form of the vessel 
in which it is kept. It possesses a sweet aromatic turpentine-like odour, especially 
when heated by the warmth of the hand. 

It is readily soluble in glacial acetic acid, ether and spirits of turpentine. 
It always contains a proportion of water. It is often adulterated largely with 
colophony. 


VENICE TURPENTINE 


Venice turpentine is obtained from the common larch (Pinus larix) which 
grows in the Tyrol and in France. It is of a bright greenish-yellow colour, and 
of the consistency of honey, and does not harden on exposure. On this account 
it is used as a softening agent in spirit varnishes. It has a sweet aromatic smell 
like turpentine. 

It melts about 110° C., and has a specific gravity of 0-856. It is soluble in 
most organic solvents, such as alcohol and ether. 


Sort REsIns 


The soft resins may be differentiated from the hard copals by their ready 
fusibility. They vary considerably as regards their hardness from gum elemi, 
which is of a soft, sticky nature, to Manila copal, which requires a temperature 
of about 135° C. to melt it. 

The soft resins are used mainly in the manufacture of spirit varnishes on 
account of their ready solubility in alcohol, turpentine and other volatile solvents. 


ELEMI 


This resin is of a whitish colour when quite pure, with a pleasant aromatic 
odour. Its specific gravity is about 1-08. 

It is obtained from various trees such as Canariwm luzonicum in Manila, 
Central, and South America, and the East Indies. 

The resin is, as a rule, of a soft and sticky nature, and although, as stated, 
generally of a whitish colour, some varieties, such as Mexican elemi, are harder 
and of a pale yellow colour. 


DESCRIPTION OF RESINS 165 


Elemi resin softens at about 80° C. and melts at 120° C. When distilled it 
yields about 10 per cent. of a mixture of volatile oils isomeric with spirits of 
turpentine. 

It is soluble in alcohol, turpentine, and most organic solvents. 

It is not used by itself in making varnish, but is added as a toughener or 
softening agent to spirit varnishes in order to make them less brittle and more 
elastic. 


Gum BENZOIN 


Gum benzoin or “ gum benjamin ” is the aromatic resin of the styrax benzoin, 
a tree which is native of Sumatra, Java, the Malay Peninsula, and Siam. 

Commercially two forms of the gum are used—one from Sumatra and the 
other, which is more highly esteemed, from Siam. 

The natives make excisions in the trees, and after about a fortnight the resin 
flows freely and is collected. 

Benzoin usually appears on the market in brownish coloured lumps, containing 
opaque yellowish white tears or almonds, with a good deal of debris of bark 
and wood. 

When warmed it gives off a strong characteristic sweet vanilla-like odour. It 
melts at about 100° C. 

It is soluble in alcohol (all except the impurities) ; in ether, turpentine, and white 
spirit it is only partially soluble. 

It is composed of resinous bodies, benzoic acid and a little cinnamic acid. On 
gently heating it melts, giving off clouds of white fumes of benzoic acid. Its specific 
gravity is about 1-14. 

Benzoin is used in spirit varnishes to impart a fragrant odour and also to improve 
and harden the gloss. 


Mastic 


Mastic is chiefly obtained from the island of Chios, one of the principal islands 
of the Greek archipelago, and is the product of the lentix tree (Pistacva lentioscus L.). 

Vertical incisions are made in the bark of the tree from which the liquid resin 
trickles, and soon becomes dry and hard. 

Mastic comes on to the market chiefly in the form of spherical or tear-shaped 
grains. It is of a pale yellow colour, inclining to green; it is very brittle, but 
softens in the mouth after long chewing, and is used in Turkey as a chewing gum. 

Its specific gravity is about 1-05. It melts at about 108° C., but softens at 
about 85° C. 

Mastic contains a resinous acid (mastic acid, C4 jH,,O,), and is soluble in 
turpentine, alcohol, acetone, but not in petroleum spirit. 

It is used in making varnish for the use of artists. Mastic varnish mixed with 
boiled oil forms a gelatinous mass known as “ megilp,” which is also employed by 
artists in oil painting. ‘ Gumption,” which is used for a like purpose, is made by 
mixing mastic varnish with a little linseed oil and sugar of lead. 


166 THE CHEMISTRY OF PAINTS 


SANDARACG 


This resin, which is also known as gum juniper, is obtained from a species of 
cypress (Callitris quadrivalis) indigenous to North Africa. In part it exudes 
naturally from the trees, but is also obtained by the Moors, who make incisions in 
the bark of the tree for the purpose of increasing the flow of the sap. 

Sandarac comes on to the market in elongated, small brittle tears, having a 
vitreous fracture, and is of a pale yellowish colour. Its specific gravity is about 
1-04. It does not soften on chewing, which distinguishes it from mastic. 

It melts at about 140° C. with a characteristic odour. I¢ is soluble in alcohol, 
acetone and ether, but only slightly soluble in turpentine and benzol. 

Sandarac is used in spirit varnishes to impart lustre and hardness. 


DAMMAR 


Dammar gum is a resin which is imported chiefly from Java, Sumatra, Siam, 
and Borneo, and is the produce of the Amboyna pine (Dammara orientalis). It comes 
into commerce in lumps, and also in nodules or grains, usually covered with a 
powdery crust, the interior of which is transparent and clear. It is friable and 
breaks easily, with a powdery fracture. 

The value of dammar gum depends chiefly on its colour, the finest qualities of 
which are nearly white in colour, or at the most of a transparent faint yellowish 
colour. 

The usual grades of Batavian dammars that come on the market are Best 
White, E, A to E (mixed grade), and Dammar Dust. The Singapore dammars are 
softer and yellower, and not equal in quality to the Batavian. 

Dammar has a specific gravity of about 1-06. It is a soft resin, and the heat 
of the hand is sufficient to make it sticky. It begins to melt at 80° C., and is quite 
limpid at 160° C. On melting it gives off a characteristic balsamic odour, by means 
of which it may be readily detected. 

It is soluble in turpentine, ether, chloroform, and in oil, but only partially 
soluble in ethyl alcohol. Solutions in turpentine have a milky turbidity, which can 
be cleared up by adding absolute alcohol. 

Dammar gum is very largely used in the varnish industry for making crystal- 
white paper varnishes, furniture varnishes, and glossy white enamels. 

Varnishes made from this gum dry with brilliant hard glossy surfaces. 
Unfortunately dammar has the defect of being rather friable, so cannot be used for 
exterior work (see Chapter III.). 


Black Dammar 


is obtained from India from a species of Canarium tree by burning the foot of the 
tree and thus causing the resin to exude. It is not used to any extent in this country 
owing to its colour. 


, 
3 
4 


DESCRIPTION OF RESINS 167 


ManitA Copa 


Manila copal is a product of various species of trees (Agathis alba) found growing 
in the Philippine and Malacca islands. It comes into commerce in two varieties 
known as spirit Manila gum and hard Manila copal. 

The spirit Manila gums are the softer varieties of the gum, melting at about 
130° C. and being wholly soluble in alcohol. In order to obtain this gum incisions 
are made in the trees, or else strips of the bark are cut off, and the exuding resin 
collected by the natives, after which they are sorted out into different grades. 

They are largely used in the manufacture of spirit varnishes. 

The hard Manila copals are old fossil remains of resins which have exuded from 
the trees at some bygone period. They are dug up, washed, and scraped ready for 
the market. Insoluble in alcohol, they do not melt below about 350° C. They are 
largely used in the manufacture of oil varnishes. 

Manila gum varies in colour from pale yellow to a deep brown. Its specific 
gravity is about 4-06. 

On distillation a large amount of frothing takes place with evolution of water 
and volatile oils, which contain pinene, limonene, and other terpenes, besides formic 
acid, acetone, and many other bodies. The acid value and the saponification value 
vary considerably according to the nature of the gum. The average figures are 
about—acid value 105, saponification value 150. 


Lac (SHELLAC) 


Lac is a resinous incrustation found on the twigs of many species of Indian trees 
(Ficus). The lac is formed from the sap of the tree by the female of the lac insect 
(Coccus lacca). 'The insect punctures the bark of the tree and secretes the lac, which 
is found hardened on the older twigs. Its colour varies from an orange yellow to a 
dark red. 

The principal portion of the lac of commerce is imported from Calcutta. It is 
sold in the following forms :— 

(1) Stick lac, (2) Seed lac, (3) Shellac, (4) Button lac, (5) Garnet lac. 


- 


Stick Lac 


is the crude product as it comes from the trees, and is mixed with bark and 
twigs. It is purified by breaking up into small pieces, thus separating the brittle 
crude lac, and washing with hot water. By this means all the colouring matter 
is extracted. The residue is dried and constitutes the seed lac of commerce. 

Seed lac is chiefly obtained as reddish-yellow grains, which as a rule contain 
very little colouring matter. 

The reddish liquor is evaporated down and sold as “lac dye,” which was 
formerly supposed to be identical with cochineal. It has, however, been found that 
the “lac dye” contains a dye called laccainic acid, represented by the formula 
Ci ¢H20s. 

M 


168 THE CHEMISTRY OF PAINTS 


SHELLAC, 


which is the principal lac product used in the varnish industry, is obtained from 
the seed lac by melting it over a fire and pouring out the easily fusible shellac 
on to revolving cylinders, from which, as it solidifies, it is scraped off in the form of 
thin brittle leaves. In this manner the more unfusible material and impurities are 
left behind. 

Properties and Uses.—Shellac is sold in various grades, named according to 
their colour, e.g. T N Orange, Fine Pale Orange, Lemon, Ruby, and so on. 

Shellac is soluble in cold alcohol, with the exception of some insoluble substances 
known as shellac-wax; in hot alcohol the wax dissolves, but on cooling it again 
separates. 

Dissolved in alcohol, shellac gives a turbid brownish-orange solution, which 
constitutes the French polish of commerce so largely used by cabinetmakers and 
others. 

Shellac is only slightly soluble in ether and turpentine. On boiling with weak 
alkaline solutions it is saponified and dissolves, giving a deep reddish solution, from 
which the shellac may again be reprecipitated by the addition of an acid. 

The specific gravity of shellac is about 1-182. 

Shellac is a tough yet brittle material, which is readily fusible (it melts at about 
150° C.), and on burning gives off a fragrant characteristic odour. It is often 
adulterated with rosin, which, however, may readily be detected by the increased 
acid value and iodine value, as also by the Liebermann-Storch test. 

The analytical constants obtained from orange shellac are approximately as 
follows :— 

Analytical Constants of Orange Shellac 


Specific gravity at 15-5° C. ; 1-182 

Melting-point . : : . 150° C. (softens at 95°) 
Acid value. : : sn Oe 

Saponification value : « BU} 

Ester value. Yon Be . 140 

Todine value . A ; ees 

Unsaponifiable : : Z 3°5 


BLEACHED SHELLAC (WHITE SHELLAC) 


As the colour of shellac is objectionable for some varnishes, bleached shellac 
is used in its place. 

Shellac may be bleached in many ways, as, for example, by treatment with 
bone black, bleaching powder, hypochlorite of soda, sulphur dioxide. The usual 
process adopted on the commercial scale is as follows :— 

Ordinary shellac is dissolved in a weak hot soda solution, and the requisite 
amount of hypochlorite of soda (made by adding a solution of soda to a solution of 
bleaching powder) stirred in. After stirring for four hours, the whole is allowed to 
stand overnight, when a sample is drawn off which should be colourless. 


DESCRIPTION OF RESINS 169 


The shellac is precipitated by adding dilute sulphuric acid, after which the 
precipitate is strained through cloths and well washed till all acid is removed. The 
white shellac thus obtained is melted under water, and then when quite soft is 
kneaded so as to give it a silky appearance. 

Bleached shellac is sold usually in the form of hanks or bars containing 
approximately 20 per cent. of water. To rid the shellac of this water as much as 
possible it is crushed and spread out in the air for a day or two. 

White shellac when dried deteriorates on keeping, becoming insoluble in 
alcohol; hence in making white shellac varnish—for which purpose it is largely 
used—it should be dissolved as soon after drying as possible. 

Bleached shellac dissolves in alcohol, giving a turbid milky solution, due mainly 
to the wax it contains, but also partially to traces of water which is always present 
in white shellac however carefully it may be dried. 

Button Lac comes on to the market in the form of round flat pieces or 
“buttons.” It is made from the crude lac in the same way as shellac, except that 
the fused shellac is run on to plates, where it solidifies into buttons about 4 to } inch 
in thickness. As a rule it is somewhat harder than ordinary orange shellac, owing 
to the small percentage of shellac wax that it contains. 

Garnet Lac is similar to button lac, but contains more colouring matter. It is 
of a transparent ruby red colour when held up to the light. 

Its value depends on the brightness and depth of its colour, for it is used for 
making coloured spirit varnishes. It is free from shellac wax, and dissolves in 
alcohol, giving a transparent deep red solution. 


(2) Tot Harp Resins (Fossit Gums) 
AMBER 


(Ambre Gris, Bernstein.) 


Amber is probably the best known of all the resins or hard gums. It was 
familiar to the ancients under the names of electrum (from which the word electricity 
is derived) and succinum. 

Amber is chiefly the fossil resin of a prehistoric conifer (Pinus succinifer) which 
grew on land now under the waters of the Baltic Sea. It is found in Denmark, 
France, and on the Essex and Suffolk coasts, but the main source of supply is the 
shores of the Baltic, where it is obtained either by dredging the sand along the 
seashore or else by mining. 

The hardest of the fossil gums, amber was at one time extensively used in the 
manufacture of the best grades of varnish ; but on account of its extreme scarcity 
and costliness it is now hardly ever used for this purpose. 

Properties.—The colour of amber varies from a pale transparent yellow to a 
dark brown colour. It is graded, like most other fossil gums or resins, according 
to its colour and the size of the pieces. 

Its specific gravity is about 1-07. When rubbed, as is well known, it acquires 
electrical properties. 


170 THE CHEMISTRY OF PAINTS 


On distillation it melts at about 350° C., and gives off water, succinic acid, and 
amber oil. It is practically insoluble in alcohol, ether, turpentine, and most other 
organic solvents. ; 


ANIMI 
(Animé.) 

Animi is extensively imported into this country for use in the manufacture of 
the highest grades of varnish. After amber it is the hardest fossil gum known, 
and the varnishes made from it are noteworthy on account of their remarkable 
hard-wearing and durable properties. 

Animi is imported from Zanzibar and from Dutch East Africa, and is the fossil 
resin remains of a tree known as Trachylobium mossambicense, which still flourishes 
in those regions. 

The gum is found at a depth of about 2 ft. in the ground, and is dug up by native 
labour during the rainy season. The resin thus collected is washed free from the red 
sand with which it is contaminated, and is then sorted out into different grades 
according to its colour. 

The best grades of animi have a pale yellowish colour, are semi-transparent, 
and are in the shape of long tears, the surface of which is covered with peculiar 
pock-marks known as “ goose-skin.” 

The specific gravity of animi is about 1-068. When held in a flame it melts, 
then ignites, burning with a clear white flame, and giving off a pungent turpentine- 
like odour. The melting-point of animi is about 300° C. 

It is not soluble in any of the ordinary organic solvents, and is unaffected by 
alkalies. 


KaAvurRI 
(Kowree, Cowdee Gum, Cawree Gum.) 


Kauri copal or gum kauri is a fossil or semi-fossil resin of various species of New 
Zealand pine trees (Dammara Australis). 

The fossil resin is found mostly in the province of Auckland in open bush land, 
where but few trees now exist. The resin is obtained by digging, after which it is 
scraped to remove all earthy matter, and then graded according to colour and 
hardness. 

Kauri comes on to the market in various grades, the best of which is known as 
“dial”? kauri, the poorest as “ bush ” kauri. 

Kauri gum is very highly esteemed, and is largely used in the manufacture of 
the best body and carriage varnishes. . 

More than two-thirds of the kauri gum shipped from New Zealand goes to 
the United States. In recent years it has become very scarce, and the price is almost 
prohibitive except for use in the manufacture of the highest grades of varnish. 

The supplies appear to be getting gradually exhausted, and probably before 
many years it will be no longer in general use. 

As a matter of interest it might be mentioned that some years before the war 


DESCRIPTION OF RESINS 171 


the labourers engaged in the industry were almost entirely drawn from Austria- 
Hungary (principally Bohemia). Every year large numbers emigrated to New 
Zealand. In fact there was a regular traffic between the two countries, for so 
remunerative was the work that many of the emigrants were able in a very few years 
to return to their native land with considerable savings. 

Propertves.—Kauri gum has a conchoidal fracture and greasy lustre. The 
poorer grades have a peculiar brown woody appearance, which is quite characteristic. 

Dial kauri is of a yellowish-white colour, powders with difficulty, and has a 
specific gravity of 1-079. 

Bush kauri, which is collected at the foot of the tree, is of more recent origin 
than dial kauri, and is of a reddish-brown appearance and easily powdered. 

Hard brown kauri gum melts at about 250° C. 

Kauri gum is insoluble in turpentine and benzol, but partially soluble in alcohol 
and chloroform. On distillation it yields about 25 per cent. of kauri oil. 


ANGOLA COoPAL 


Angola copal is a somewhat soft fossil gum, which is found in Angola, on the 
west coast of Africa. The best qualities reach the market in the form of large irregular 
lumps, known as white Angola copal, which is of a pale semi-transparent white 
appearance, and is used for making pale copal varnishes. 

Its specific gravity is 1-062. It melts at about 210°C. Angola copal of a 
reddish colour is also put on the market, and is sold under the name of red Angola 
copal. 

S1eRRA LEONE Copa 1 


This fine resin is imported from Sierra Leone (West Africa). It is not fossil, 
but is produced by a leguminous tree called Gucbourtica copallifera, and is collected 
in the same way as turpentine is in France. The pieces are irregularly spherical 
or elongated, usually small, and of a yellowish to a clear white colour. It is easily 
powdered. Its specific gravity is about 1-054. It melts at about 185° C. 

It is used in the manufacture of the palest French oil varnishes. 


PoONTIANAC 


This fossil gum is imported from Borneo, and comes on to the market in the 
form of large irregular-shaped lumps, varying in colour from a semi-transparent 
pale yellowish-white to a reddish-brown colour. 

It is of a very hard glassy nature, and on being hit with a hammer splinters off 
into small pieces, which may be readily powdered. 

Its specific gravity is about 1-062. It melts at about 280° C. 


BENGUELA COPAL 


This copal is obtained from equatorial Guinea, south of Angola, on the west 
coast of Africa. It is put on to the market in irregular lump form, and has a 
semi-transparent yellowish colour. 


1 A. Foelsing, ‘‘ Chem. Rev. Fett-Harz-Ind.,” xiv. 251. 


172 THE CHEMISTRY OF PAINTS 


It is a comparatively hard gum and is difficult to break; the fracture is of a 
brilliant glassy appearance. It melts at about 260° C. 


Congo CoPaL 


Congo resins are imported from the Belgian Congo. They are hard fossil gums, 
the colour of which varies from a semi-transparent pale whitish yellow to reddish 
brown. 

It is very hard to fuse (its melting-point is 300° C.), and a considerable amount 
of volatile matter must be driven off before it will amalgamate with linseed oil. 
It breaks with a conchoidal fracture, with a shiny glassy lustre. 

On account of the large supplies available, Congo gums are comparatively 
cheap, and are now being largely used in the manufacture of varnishes. 


CoLouRED RESINS 


For the sake of completion it is perhaps desirable to give here a brief description 
of some of the more important of the very many naturally-occurring coloured resins 
and woody fibres, such as gamboge, dragon’s blood, grass tree gum, red and yellow 
sanders wood, and others, which were formerly largely used for the purpose of 
colouring spirit varnishes. 

These natural coloured resins have now been largely replaced owing to their 
lack of permanency by the synthetic coal tar dye-stufis, and are now only used in 
special cases. 


Rep SanperRs Woop 
(Red Sandal Wood, Pterocarps Lignum.) 


Red sanders wood is the heart wood of Pterocarpus santalinus. It is imported 
in large heavy logs of a dark reddish-brown colour, the colouring matter of which 
is readily soluble in alcohol, but only sparingly soluble in water. For use in spirit 
varnishes the logs are cut up into chips, or, more often, rasped into a fine powder. 


GAMBOGE 
(Cambogia.) 


Gamboge is a gum resin from Garcinia Hanburii, which grows in India, Ceylon 
and Siam. It is usually obtained as a yellowish-brown milky juice, which hardens 
in the air, by making incisions in the bark of the tree. 

It is marketed in the form of lumps, cakes and sticks ; is rather brittle and often 
covered with a yellow dust. 

Gamboge contains about 80 per cent. of resin or gamboge yellow (C,,H,,.0.) 
which is readily soluble in ammonia, alcohol, or ether, giving a yellowish solution, 
which is distinctly acid. 

It is used as a water colour by artists and also as a colouring matter in spirit 
varnishes and in making gold lacquer. 


DESCRIPTION OF RESINS 173 


Dracon’s Bioop 


This comes from various species of plants, but chiefly from the fruit of the 
Calamus drago of Sumatra, Indo-China and Molucca. 

The brittle red resinous mass is obtained by shaking the ripe fruits into baskets 
and sifting out the impurities. The resin is then melted and moulded into sticks 
or cakes. 

The best qualities have a deep blood-red colour. The specific gravity is about 
1-25, and contains about 60 per cent. of a red resin. It has a peculiar acrid taste, 
and is readily soluble in alcohol, giving a blood-red solution. 

It was formerly much used for colouring spirit varnishes, but is being 
gradually superseded for this purpose by the soluble spirit red aniline colours. 

It melts at 100° C., emitting vapours of benzoic acid. 


Gum AcOROIDES 
(Acaroid Resins, Black-boy Gum, Grass-tree Gum.) 


These resins are the product of various species of trees indigenous to Australia, 
such as Xanthorrhea Australis. ® 
There are two varieties, one the yellow gum accroides, and the other the red 
variety. Both varieties are soluble in alcohol. They are sometimes used for 
colouring spirit varnishes. 
Lac 


This natural-coloured resin has been described under Shellac. 


CHAPTER XVI 


DRYING OILS 


Drying oils is the name given to those oils which possess the property of forming 
a solid elastic substance when exposed to the air in thin films, e.g. linseed oil and 
wood oil. This drying property is due to these oils gradually absorbing oxygen 
from the air, and decreases as the iodine absorption value of the oil diminishes. 
When a drying oil is converted into a solid elastic film it is said to “ dry.” 

A non-drying oil, such as olive oil and castor oil, on the other hand, will remain 
liquid at room temperature for an indefinite period. 

Semi-drying oils, like cotton-seed oil and maize oil, lie between the two. 

By far and away the most important of the drying oils is linseed oil, which is | 
used in enormous quantities in the paint and varnish industries. 


LINSEED OIL 


Linseed oil is obtained from the seeds of the flax plant Linum usitatissimum 
which is grown in large quantities in the Argentine, India, United States, Canada 
and Russia. 

The seeds are brown in colour, and contain 36 to 42 per cent. of oil, practically 
all of which may be extracted with the aid of suitable solvents. 

Linseed is imported into this country chiefly from the Argentine (Plate oil) 
and India (Calcutta oil). The seed grown in Canada and the United States is used 
for home consumption. 

Formerly large quantities of linseed were imported from Russia (Baltic 
oil), and owing to the purity of this seed the oil extracted therefrom was 
highly valued, being much superior as regards “drying properties to either 
Plate or Calcutta oil. 

As linseed oil is mainly used in the paint and varnish industries, the relative 
drying properties of the oil extracted from the different seeds imported is of the 
utmost importance. The variation in the drying properties of the different linseed 
oils is due mainly to the linseed containing other foreign seeds mixed with it, such 
as hemp, rape and mustard. 

Composition.—To determine the relative proportions of the constituents in 
linseed oil is a problem which presents great difficulties. According to Fahrion * 
the average composition is approximately as follows :— 

1 Fahrion, Zeitsch. Angew. Chem., 1910, 23, 1106. 
174 





(‘py] ‘uosdwoyy, Y sumog ‘esoy) “ANIHOVIK 
ONIGTAOW WVALG HLIM SUYMMOO/) YO SAILLGY ONILVAY GAASNIT—'CZ “DI ‘STIOY NVOIUANY-OIDNY—'PzZ ‘OLA 











DRYING OILS 175 


Unsaponifiable matter. : : . 0-6 per cent. 

Saturated organic acids é : : reeds - 

Oleic acid . : : : . : se Wes: z 

Linolic acid . , , ; F . 30-0 - 

Linolenic acid . : : : ; . 938-0 ‘id 

Glyceryl radicle . ; ; ; : . 4:6 Xp 
100-0 


EXTRACTION OF LINSEED OIL 
Linseed oil can be extracted from linseed either by means of solvents or else 
by pressure. The highest yield of oil is obtained when the extraction is carried out 
by the aid of solvents, but the resultant ‘“‘ cake ”—which is a valuable by-product 
—is unsuitable for cattle feeding. Hence the method employed in practice is to 
extract the oil by pressure ; when this is done about 10 per cent. of oil is left in the 
press cakes. 


Extraction by Pressure 

The early methods in vogue for expressing linseed oil were very crude, and 
simply consisted in packing the linseed in bags and squeezing out the oil by means 
of hand-presses. 

At the present time the bulk of the linseed oil that comes on to the market 
is obtained by the Anglo-American system, in which powerful hydraulic presses 
are used, by means of which a pressure from 2 to 3 tons per square inch can be 
obtained. } 

The first stage in the Anglo-American process is the crushing of the linseed. 
The linseed is fed into a hopper, and passes through a series of four or five revolving 
chilled-steel rolls, whereby the seed is crushed into an extreme fine state of sub- 
division (Fig. 24). The crushed seed (‘‘ meal’) is then conveyed to a cast-iron steam 
jacketted kettle (Fig. 25), where the seed is heated to about 180° F., and agitated 
by a revolving stirrer. Steam is blown into the mass in order to moisten it to the 
requisite degree. 

The cooked linseed meal is next moulded into cakes of uniform size, conveyed 
to the Anglo-American press, where it is subjected to a pressure of about 1? tons 
to the square inch (Figs. 26 and 27). 

The oil thus expressed is pumped into large storage tanks; it is as a rule 
turbid owing to the presence of albuminous and mucilaginous matters; but after 
standing about a week the impurities settle out, and the oil becomes perfectly clear 
and transparent, when it is ready for use. The “spawn” or mucilage which settles 
out on tanking contains phosphates of lime and magnesia. 

The actual yield of oil obtained by this process is about 28-30 per cent. 


Extraction by Solvents 
This process gives the highest yield of oil, but the resulting “ cake ”’ is not suit- 
able for cattle feeding, not only on account of its low oil content, but also because 
it is extremely difficult to remove completely all traces of the solvents used. 


176 THE CHEMISTRY OF PAINTS 


On this account this process is only used in those cases where the seed is in very 
bad condition due to bad storage conditions, either before or during shipment. 

In this process the crushed seed is packed in perfectly air-tight vessels, 
through which the solvents flow. The 
solvent is continuously distilled off by 
steam, condensed, and returned to the 
extracting vessels till all the oil has been 
extracted, when the vessels are emptied 
and recharged with a fresh supply of 
crushed seed (Figs. 28 and 29). 

The solvents in most general use are 
petroleumether, carbon di-sulphide, carbon 
tetrachloride, and trichlor-ethylene. 

Properties and Uses.—Cold-pressed 
oil is of a light-yellowish colour, with a 
characteristic pleasant odour and taste. 

Warm-pressed oil is of a yellowish- 
brown colour, and the taste and odour are 
more pronounced and not quite so agree- 
able as in the case of the cold-pressed oil. 

The specific gravity is about 0°930- 
0:931 at 15°5° C. (Baltic oil is 0-934). 

Linseed oil differs from most other 
vegetable oils in remaining liquid at 
0° C. and below. It thickens at about 
—19°C., and at about —29° C. solidifies 
to a solid yellow substance. 

When heated it gives off pungent 
vapours containing moisture and acrylic 
acid. It flashes at 260° C. 

Linseed oil is readily soluble in 
ether, turpentine, chloroform and similar 
solvents; but only partially soluble in 
alcohol. 

Fig. 26.—AnaLo-AMERIcAN PREss. Strong sulphuric acid rapidly chars 
_ linseed oil causing it to become thick and 
of a black colour. Strong nitric acid converts it into a viscous, yellowish mass. 

Linseed oil readily absorbs iodine and bromine owing to its high content of 
glycerides of unsaturated acids. The iodine value is one of the readiest means 
of determining the purity of a linseed oil. 

When exposed to the air in a thin film, linseed oil gradually absorbs oxygen, 
ultimately yielding a solid elastic mass known as linoxyn. 

This oxidation product is highly resistant, and is very insoluble in most oil 
solvents. It is on account of this property, and the brightness and elasticity of 


Ses zh 


7 
+E 
1 
io 
WN | GK 
SS! 


st 














Fic. 27.—View or SoLip ROLLED STEEL PRESS PLATES, AS SUPPLIED WITH ANGLO-A MERICAN PRESS, 
SHOWING ELEVATION, LONGITUDINAL HLEVATION AND CROSS SECTION OF THE PLATES BENT COLD. 





Fig. 28.—Om EXTRACTION BY SOLVENTS—VIEW SHOWING 
EXTRACTION VESSELS, CONDENSER, EVAPORATORS, ETC., 
IN Larce Extraction Prant. (Rose, Downs & 
Thompson, Ltd.) 





oe = re or mi | awh. tat ‘ =", Sie ; | "s 1th £ ce 


n mer ae ya Chg Dey. ts : r 
, i ee ey oe ae : ; 
roy EA ae } leo ee 
, aE tye - — > ee Seal = 3 ; 
— mens ty : 
. ; - 
~.,) ales 1) 2" 
é ia | 
i 
2 \ | an ‘- ~ 
‘ a 5 








Fig. 29. 
IN Lance Extraction Puant. (Rose, Downs & Thompson, Ltd.) 


Or EXTRACTION BY SOLVENTS—EVAPORATORS AND CONDENSERS 


DRYING OILS 177 


the skin so formed, that linseed oil is so valuable as a vehicle for paints and 
varnishes, and in the manufacture of lmoleum and waterproofing materials. 

If thin glass or aluminium plates are coated with a thin film of linseed oil, 
weighed, and then placed in a dust-free atmosphere in a room of uniform 
temperature, and weighed at intervals of 12 hours, it will be found that there is 
a period of induction when no appreciable change of weight takes place. After 
this period a rapid increase of weight takes place, which rises to a maximum after 
about 100 hours, after which the oil very slowly loses in weight. 

The increases in weight show considerable variation, namely, from 14 to 
26 per cent., the average amount being 18 per cent. The value thus obtained 
is known as the “ Oxygen figure.” 

It has been shown that while this increase of weight is gomg on—due to the 
absorption of oxygen—decomposition is taking place and gaseous products are 
being evolved. 

The chemical composition of the vapours evolved from linseed oil during drying 
have been fairly accurately determined. It has been shown that water constitutes 
the bulk of these products, together with traces of carbon dioxide, formic acid, 
acetic acid, acrylic acid, butyric aldehydes, and a minute trace of carbon monoxide. 

Linseed oil, besides being extensively used in the paint, varnish, and linoleum 
trades, is also used in the manufacture of soap and putty. 

Linseed oil is extensively “ hardened ” by hydrogenation, with a nickel catalyst, 
producing a very fine hard stearine, which is largely used in the soap and margarine 


industries. 
Average Analytical Constants for Linseed Oil 


Specific gravity at 15-5° C. ; : ; . 0-930-0-934 

Acid value ; : ; : A : 6-0 
Saponification value . ; : ‘ ‘ LEO 

Todine value (Wijs) . : ; : : . 180-185 
Refractive index 40 C°(ZB) : : scl 6 
Unsaponifiable matter : ; : : d 0-5-1-5 per cent. 
Solidifying point of fatty acids . : : pS i gab 


SCHEME FOR THE ANALYSIS OF LINSEED OIL 


Raw linseed oil obtained from the oil mills may be taken to be commercially 
pure. It is rarely if ever found to be adulterated, in spite of the formidable list 
of adulterants such as rosin oil, mineral oil, fish oil, and many others enumerated 
in the various text books dealing with the subject. 

Without recourse to tedious methods of analysis, the taste and smell of the 
oil alone should be quite sufficient to indicate the presence of these adulterants if 
existent in more than minute quantities. 

An adulteration with 10-20 per cent. of soya bean oil would be more difficult 
to detect, but in this case the retardation of the drying properties, accompanied 
by the decreased iodine value, would readily reveal its presence. 


10, A. Klein, Chem. World, 1914, 3, 250. Gardner, J. Ind. Eng. Chem., 1914, 6, 91. 


178 THE CHEMISTRY OF PAINTS 


Hemp seed oil might also be used, but its value as a rule approximates to 
that of linseed oil. 

When it is desired to test the purity of linseed oil, and its suitability for use in 
the manufacture of paints and varnishes, the following tests should be carried out 
(Note-—This scheme of analysis is also applicable to all animal and vegetable oils) :— 


(1) Sprcrric GRAVITY 


Take a 50 c.c. gravity bottle (Fig. 21), and weigh it accurately to four decimal 
places. Fill with distilled water, and place in a water bath maintained at 15-5° C. 
for 15 minutes. Insert the stopper and remove the water that oozes from the top. 
Dry quickly with a clean dry cloth, holding the bottle by the neck, and weigh. 
Repeat this operation so as to make quite sure the result is correct. By this 
means the volume of the bottle is accurately determined once for all and the 
necessary + correction factor found. 

The bottle is next emptied and carefully dried in the steam oven. Linseed 
oil is next introduced, and the method of cooling, drying, and weighing carried 
out precisely in the same manner as in the case of the water. 

As the specific gravity is the weight of any volume of a substance compared 
with the weight of an equal volume of pure water at a standard temperature 
(15-5° C.), all that is necessary is to divide the weight of the oil obtained by that 
of the weight of an equal volume of water. 








Example. 
Weight of 50 c.c. gravity bottle ; ; , . 25-5301 gms. 
a x x + water at 155°C. . ., E503 a3, 
»» water at 15-56° Ce, : : , : . 49-9202 ., 
» bottle + linseed oil at 15-5° C. . : ‘ . 72°0602 ,, 
» bottle . ; . ‘ : : : . sepa hee. 
jy « oll'at 1b? CN : ; , : : . 46-5301 ,, 





Weight of linseed oil at 15-5 C._ 46-5301 __, 9899 specific eravity of Een am 
Weight of water at 15-5° C. = 49-9202 


or shortly, as correction='080 weight of linseed oil=46-5301-+-080=46-6101 x2 
=93-2202 .-. specific gravity of linseed oil=-9322. 

The specific gravity may also be obtained by weighing the oil in a Sprengel 
tube, by the Westphal balance, or by means of hydrometers. 





(2) Actb VALUE oR FREE ACIDITY 


Free acidity equals the percentage of oleic acid present in an oil. 
N 
1 ce. 7 KOH=0-282 gms. oleic acid. 


Acid value equals the number of milligrams of potassium hydrate required 
to neutralise the free fatty acids in 1 gm. of oil. 


DRYING OILS 179 


N Determination of Free Acidity 
5 KOH or Na OH (aqueous solutions) are the best. 


Weigh out about 15 gms. (quantity optional). Dissolve in 50-66 c.c. neutral 
alcohol, and titrate with KOH solution, using phenol phthalein as indicator. 


Although linseed oil is only partially soluble in alcohol, the free fatty acids are 
generally very much more soluble. 

If preferred the oil may be dissolved in methylated ether, and the neutral 
alcohol then added. 

If mineral acids be present these can be neutralised by the potash, using 
methyl orange as indicator ; and when the solution has turned from red to yellow 
the titration can be continued with phenol phthalein as the indicator. 


(3) SAPONIFICATION VALUE 


The saponification value is the number of milligrams of potash required to 
saponify one gram of oil. The number of grams of oil saponified by one equivalent 
of potash, 7.e. 56-1 grams of potash, is termed the saponification equivalent. 

Free fatty acids in an oil raises its saponification value; whilst on the other 
hand any considerable quantity of unsaponifiable matter proportionately reduces 
this figure. The determination of the saponification value of linseed oil is carried 
out as follows :— 


N 
Solutions y HCl (z.e. 1-325 Na,CO, to 50 c.c. HCl solution). 


a 2 approx. potash hydrate in redistilled alcohol; made by dissolving 


35 grams of potash hydrate (pure by alcohol) in 1 litre of alcohol. 

Weigh out under 4 grams of the oil, run in 30 c.c. alcoholic potash solution. 
Boil, with frequent shakings, under a reflux (a long, wide glass tube) till the 
solution is quite clear. 

Tf mineral oil be present, it will remain undissolved, or separate out on 
cooling the flask. 


: 
Titrate the excess potash by 2 HCl solution. Do a blank under the same 
conditions. It is not necessary, unless preferred, to add any water before titration. 
Number of c.c. s HCl for blank minus number of c.c. = HCl used in titrating 


excess of potash x by 28 divided by weight of oil taken equals saponification 
value. 
(4) UNSAPONIFIABLE MATTER 
Weigh out 5 grams of the oil into a 6-inch porcelain basin. Add 25 c.c. of 2 N 
alcoholic NaOH solution, and evaporate the alcohol gently, with occasional stirring, 
to dryness. 


180 THE CHEMISTRY OF PAINTS 


Add a further 25 c.c. of alcohol and 2-5 gms. pure soda bicarbonate (NaHCO,) 
and again evaporate to dryness. Just before this point is reached stir well in 
50 gms. ignited sand, and place in water oven for one hour till no smell of 
alcohol is perceived. 

Extract in a soxhlet (see Fig. 7) with methylated ether till all the unsaponifiable 
matter is taken out. Wash this extract with warm water to wash out any 
dissolved soap. Generally three washings are sufficient. Always have a large 
bulk of ether present to lessen the error due to the washing. Then distil off the 
ether in a tared vessel and weigh. 


Examination of the Unsaponcfiable 


In pure linseed oil the unsaponifiable rarely exceeds 1 per cent. This also 
applies to most oils with the exception of rosin oil, marine animal oils, such as 
sperm, porpoise, shark-liver, and a few other oils. 

If the unsaponifiable be alcohols, they are soluble in cold ethyl alcohol. 
This is not the case with most mineral oils. 

Alcohols and cholesterols, etc., are soluble in boiling acetic anhydride (do this 
under a reflux, boiling for two hours). 

Rosin oil gives the characteristic test with the Lieberman-Storch reaction 
(acetic anhydride+1-53 sulphuric acid) ; also, rosin oil will dry. 

If soap is thought to be present in the unsaponifiable it may be ashed, when 
sodium oxide Na,O is left—otherwise there should be no ash. 


(5) lopinE VALUE 


The iodine value of linseed oil is of the utmost importance in determining 
its purity. 

Hibl in 1884 found that by dissolving an oil in a suitable solvent, such as 
chloroform or carbon tetrachloride, and adding a solution of iodine and mercuric 
chloride in 95 per cent. alcohol, iodine is absorbed fairly rapidly during the first 
two hours, and more slowly afterwards. In about twenty hours absorption is 
complete. By taking a known quantity of iodine, and estimating with thiosulphate 
the excess remaining behind when the reaction is complete, the amount absorbed by 
100 gms. of oil may be readily determined. This is known as the iodine value. 

The iodine value depends on the proportion of unsaturated fatty acids present ; 
the higher the iodine value, as a rule, the greater the drying properties of the oil. 

Perfectly pure saturated acids and glycerides have no iodine value. 

It is generally assumed that a chloro-iodo addition compound is formed, one 
atom each of chlorine and iodine attaching themselves to the carbon atoms at 
each double bond, thereby yielding saturated derivatives. 

Hiibl’s process for the determination of the iodine value, owing to the long 
period required for the complete absorption of the iodine, has now been replaced 
by modifications such as those of Wijs and Hanus whereby the action is complete 
in from two to three hours. 


DRYING OILS 181 


The Wijs modification is the one in general use in this country and is carried 
out as follows :-— 


Solutions 


ICl Solution.—Dissolve 7-2 gms. of iodine and 7:35 gms. of iodine trichloride 
in a litre of pure glacial acetic acid. 

Ki Solution—Dissolve 10 gms. of potassium iodide in 100 c.c. distilled 
water. 

Lhiosulphate Solution—Dissolve 23:5 gms. of pure sodium hyposulphite 
in a litre of water, of such a strength 
that 30 c.c. IC] solution requires 50 c.c. 
Na,S,0, solution. 

Weigh out 0-15 gms. (7 drops) of the 
oil into a clean dry 12-0z. bottle, provided 
with a ground glass stopper. 

To weigh out the oil accurately, cut off 
a small piece of tube + inch long, seal one 
end, and flatten out while hot so that it will 
stand upright, and use this as the oil con- 
tainer. Introduce the right amount of oil 
and accurately weigh; then slide gently 
into the 12-oz. bottle. 

Now add 10 c.c. pure carbon tetra- 
chloride and run in 30-1 cc. ICl solution 
(and count as 30 c.c.), shake gently, 
and place in a dark cupboard for one 
hour. 

Do a blank under the same conditions. 

Then add 10 c.c. by pipette 10 per 
cent. K1 solution and 100 c.c. water. 
Shake well, and titrate the excess iodine 
by the Na,8,0, solution, using starch as 


indicator. Fic. 30.—REFRACTOMETER. 


Hanus Method 


This method is largely used in America, and is carried out as follows :— 

Dissolve 13-2 gms. of iodine in 1000 c.c. of pure glacial acetic acid. Add 
enough bromine to double the halogen content, determined by titration—3 c.c. of 
bromine is about the proper amount. Proceed as described under the Wijs process. 

In both processes it is necessary that a large excess (50 per cent.) of iodine 
should be present. 

Wijs solution may also be made by dissolving iodine in pure glacial acetic 
acid and passing in dry chlorine till the iodine is converted into iodine mono- 
chloride (ICl). 





182 THE CHEMISTRY OF PAINTS 


(6) Rerractive InpEx 


The refractive index is of great value in determining the purity of linseed oil, 
and is preferred by some chemists even to the iodine value. 

It is determined by using a properly standardised refractometer such as the 
Pulfrich, Abbe or Butro-Refractometer (Fig. 30). 


Qualitative Tests on Raw Linseed Oil 


Rosin.—Rosin, or rosin oil, may be readily detected if present by the 
Liebermann-Storch test, which is carried out as follows :—Gently warm a small 
portion of the linseed oil with an equal volume of pure acetic anhydride; cool ; 
pipette off the acetic anhydride layer, and add to it one drop of sulphuric acid 
S.G. 1-53 (by mixing 34-7 c.c. conc. sulphuric acid with 35-7 c.c. of water). In the 
presence of rosin a fugitive violet coloration is produced. 

The amount of rosin present may be estimated, if required, by the Twitchell 
method. In this process the sample of oil is saponified, and then treated with 
mineral acids whereby the fatty acids and rosin acids are liberated. 

The dried mixed fatty and rosin acids are weighed accurately, and dissolved 
in ten times their volume of absolute alcohol, and saturated with dry HCl gas. 
The fatty acids are converted into esters, while the rosin acids are unaffected. 

The esters and rosin acids are washed free from acid, dissolved in alcohol, and 
titrated with N alkali, using phenol phthalein as indicator. 

Number of c.c. of alkali required x0-346=rosin acids present. 

Mineral Oil.—Take a large boiling tube half full of alcohol (90 per cent.) and 
add a piece of caustic potash (pure by alcohol) about the size of a pea and warm 
till dissolved. Add 3 drops of linseed oil and boil for three minutes, allowing the 
alcohol to rise well up to the sides of the tube. Fill up with distilled water. 

The solution will be perfectly clear unless mineral oil is present, when a milky 
white solution is obtained. 

Cotton-seed Oil.—This is detected by the Halphen colour test, which is carried 
out as follows :— 

Make 1 per cent. solution of flowers of sulphur in carbon bisulphide and add it 
to an equal volume of the oil dissolved in its own volume of amy] alcohol. 

Stand in boiling water for about ten minutes, when a deep red coloration is 
produced if any cotton-seed oil is present. 

Fish Oils—Add 2 drops of conc. sulphuric acid to the oil. If fish oils be 
present a purple brown coloration is produced. 


Specification for Raw Linseed Oil 


(1) The oil must be of clear transparent pale yellowish colour, and have a 
pleasant odour and taste. It must not be turbid or contain any foots. 


DRYING OILS 183 


(2) The oil must be genuine and free from admixture with mineral or other oils. 

(3) Three drops spread out evenly ona piece of ground glass 4 in. by 3 in., and 
placed in a water oven at 100° C. must dry to a hard film in sixty minutes. 

(4) The specific gravity of the oil at 15-5° C. must not be less than 0-930 nor 
greater than 0-936. 

(5) The refractive index of the oil at 40° C. (Z B) should be not less than 72 
nor greater than 74. 

(6) The acid value of the oil must not be greater than 4. 

(7) The saponification value of the oil must not be less than 187 nor greater 
than 195. 

(8) The oil should contain not more than 1-5 per cent. of unsaponifiable matter. 

(9) The iodine value of the oil (determined by the Wijs method) should not 
be less than 175. 

(10) On ignition the oil should not yield more than 0-25 per cent. of ash. 


REFINED LINSEED OIL 


Raw linseed oil which comes from the press is always turbid and is tanked so 
as to clear itself and get rid of water and mucilaginous impurities, which settle to 
the bottom of the tank as foots. 

The colour of this oil is too deep for many purposes, and hence it is subjected 
to a refining process so as to bleach out a lot of the colouring matter present. 

For artists’ oil it is usual to expose the raw oil in shallow tanks covered with 
glass to the sunlight over a period of three or four months, whereby the chlorophyl 
and allied compounds, which cause the deep colour of the crude oil, are bleached 
out, leaving an oil of a very pale colour. 

For ordinary commercial purposes, however, it is usual to refine it in the 
following manner :—5 to 10 tons of oil are pumped into a large tank fitted with 
blowers so as to agitate the oil thoroughly. About 14 to 2 per cent. of fairly conc. 
sulphuric acid is then added to the oil, which is well agitated; the mucilaginous 
matter is thereby partially charred, and as it sinks to the bottom it carries other 
suspended impurities with it. Water is next run in, and the whole mass well 
agitated by blowing in air, and then allowed to settle for twelve hours. The black 
oily mass that separates out at the bottom is known as “ black strap oil” and is 
run off with the water. 

The oil is again well washed with hot water to remove any traces of acid that 
may be present, allowed to settle, and drawn off into tanks ready for use. 

Refined oil is used in all those cases where the colour of the ordinary raw 
linseed oil would be objectionable, such as in the grinding of white lead and other 
white pigments. 


BortED Ort or BorwED LINSEED OIL 


The reason why linseed oil is so valuable a medium in the paint and linoleum 
trades is on account of its drying properties, due to its high content of glycerides of 
unsaturated acids. 

N 


184 


THE CHEMISTRY OF PAINTS 


Linseed oil when spread in thin films absorbs oxygen from the air and is 
converted into “linoxyn,” a tough elastic body which is very insoluble and not 
readily acted on by chemical agents, and has a composition represented by the 


formula C,.H. 


57 92 


Oe. 


This property of absorbing oxygen is greatly increased by heating the oil to 













BS 
Lanaell 








= 
AA ZTIITVA\WSSss 
— 











































Fig. 31.—Linsrep Om Bormine Pan, 
HEATED BY STEAM. 





about 300° F. or higher in the presence 
of certain metallic oxides, such as the 
oxides of lead, manganese and cobalt. 

These oxides are known as siccatives 
or dryers (see Chapter XX.), and if they 
are suitably chosen and used in the right 
proportions, and at suitable temperatures, 
enable the linseed oil to dry to a hard 
film in about eight hours instead of two 
or three days, which is the normal time. 
This is of the utmost importance in the 
paint, varnish and linoleum trades. 

Linseed oil which has been heated 
with dryers is known as boiled oil. 

The metallic oxides act as oxygen 
carriers or catalysers, accelerating the 
speed at which the oil absorbs oxygen 
from the air, and thus the formation of 
“ Tmoxyn.” 


Borne LiInsEED OIL 


The oil according to the old- 
fashioned method was heated by direct 
fire heat in iron or copper pans to about 
300-400° F., and the driers, consisting of 
litharge, red lead, and manganese dioxide, 
stirred in till completely taken up. 


By this means a heavy-bodied dark boiled oil was produced, which dried in 


about eight hours with a tough hard film. 


Fire-boiled oil is still preferred in some trades, such as, for example, in the 
manufacture of waterproof sheetings, on account of its hard drying qualities. 

In a modern oil-boiling plant the usual process consists in heating from 5 to 10 
tons of oil at a time in large iron pans, provided with stirrers and blowers, and _ 


heated with superheated steam (Fig. 31). 


The oil is pumped into the pan until it is three-quarters full, and is heated 
with steam, whereby the temperature of the oil is gradually raised. At about 
220° F. a considerable amount of frothing takes place, due to the evolution of 


moisture in the form of steam. 


DRYING OILS 185 


At about 300° F. the stirrers are set going and the requisite amount of driers 
added. 

The driers in general use are mixtures of lead and manganese resinates or 
linoleates, but the resinates or linoleates of cobalt may also be used. 

The oil is now blown, and the temperature is maintained at about 300° F. for 
eight hours. Samples are drawn off from time to time. When the required colour 
is obtained, then the stirrers are stopped and the steam and blowers shut off, and 
the whole left for twelve hours to settle out. 

During the process of boiling the oil undergoes some decomposition. Water is 
continually being given off, accompanied by large quantities of acrolem C,H,,CHO, 
a derivative of glycerine, which is recognised by its penetrating acrid odour and by 
its powerful action on the lachrymal glands of the eye. 

The quantity of driers used depends on the kind of oil that is required—that 
is, whether pale or dark. Care should be taken not to use excessive quantities of 
driers, as these would accelerate the rate of drying to such an extent that the films 
produced from such oils would be crinkly and spotty. 

The function of the manganese, lead and cobalt driers in boiling oil is to take 
up oxygen from the air and transfer it to the oil; and in so doing they undergo 
alternately the process of oxidation and reduction. 


Properties and Uses of Boiled Oil 


Boiled oil varies in colour from a pale straw yellow (bleached boiled oil) to a 
dark reddish colour (double boiled oil), according to the nature and amount of driers 
used and the temperature at which the oil has been boiled. 

The specific gravity varies from 0-940 to 0-950, and the time of drying from 
eight to twenty-six hours. 

The following grades of boiled oil come on to the market :—Double boiled oil, 
single boiled oil (¢.e. ordinary boiled oil), pale boiled oil, bleached pale boiled oil. 

On account of its rapid drying property boiled oil is largely used as a paint and 
varnish medium, and also in the linoleum trades. 


Specification for Boiled Oil 


1. The boiled oil must be pure old tanked boiled linseed oil, transparent, and 
equal in depth of colour to the standard. It must not contain foots or other 
suspended matter. 

2. The oil should be free from admixture with mineral oils or any other oils, 
and contain not more than 2 per cent. of rosin or resinates. 

3. The specific gravity at 15-5° C. must not be less than 0-940 nor greater than 
0-950. 

4. A thin film of the oil when spread out on glass should dry at ordinary room 
temperature in not more than twenty-four hours. 

5. The acid value of the oil should not be greater than 6. 

6. The iodine value of the oil (Wijs method) should be not less than 170. 


186 THE CHEMISTRY OF PAINTS 


7. The oil should not contain more than 2 per cent. unsaponifiable matter, 
and on ignition should not give more than 1-5 per cent. of ash. 


Scheme for the Analysis of Boiled Oils 


The analysis of a boiled oil should be carried out according to the scheme given 
for the analysis of raw linseed oil. 

Boiled oils are much more liable to be adulterated than raw oils, the usual 
adulterants being a small amount (1-2 per cent.) mineral oil, rosin oil, or more 
usually an excessive amount of rosin in the driers; also soya bean oil, menhaden 
oil, and any other drying oil that should happen to be cheaper than linseed oil at 
the time when the oil is boiled. 

Bung Boiled or Bung-hole Boiled Oils.—This is the name given to linseed oil 
to which about 10 per cent. of terebine has been added to make it dry somewhat 
hike boiled oil. These oils generally contain a lot of foots, and their drying 
properties are very unsatisfactory. 

Raw and Boiled Oil Substitutes—When linseed oil is high in price large 
amounts of raw and boiled oil substitutes are put on the market, and extraordinary 
claims are made as to their value. 

As a rule these substitutes are of very little value, and cannot be regarded 
in any way as being equal to linseed oil or capable of replacing it except in the 
case of the cheapest class of export paints. 

These substitutes are usually made from common rosin which has been 
treated so as to render it non-feeding, and thinned down with an equal weight 
of petroleum thinners. In addition they sometimes contain about 10 per cent. 
of fish oil to help to soften the rosin and make it less brittle. 

The better class of linseed oil substitutes are frequently made by thickening 
linseed oil or fish oils (or a mixture of both) by blowing with air, or by treatment 
with sulphur, till a very thick-bodied oil is produced. This is then thinned down 
to the right consistency with petroleum thinners. In the case of the boiled oil 
substitutes—as will be understood—it is necessary to add a comparatively large 
quantity of lead and manganese driers in order to get the desired drying properties. 

The following analyses by the author of “ Raw and Boiled Oil Substitutes ” 
will give an indication of their composition :— 


1 2 
Raw Oil Substitute. Boiled Oil Substitute. 

Specific gravity at 15:5° C. . 0-930 0-932 
Acidity (oleic acid) : : . 260 per cent. 22 per cent. 
Unsaponifiable on the residue . . 12-20 - 12-89 * 
Loss on heating (white spirit) . . 46-6 f 43-0 S 
Residue (rosin-+-approx. 10 per cent. 

mineral oil) : Aged . Dore e 57-0 en 


The raw oil substitute contained a trace of lead, whilst the boiled oil substitute 
contained about 2-5 per cent. of lead and about -5 per cent. of manganese (Mn). 


DRYING OILS 187 


3 
Boiled Oul Substitute 
Specific gravity at 15-5° C. : : : -938 
Acidity (as oleic acid) . : ; . 35 per cent. 
Loss on heating (white spirit) . : . 48-50 3 
Residue : : : : j . 51-50 a 


The residue consisted of a thickened oil, with a very small amount of rosin, 
and contained lead and manganese driers. 


CuinESE Woop Oi (Tune Oiz) 


Tung oil is obtained from the seeds of Aleurites cordata, which grows in China, 
Japan and Cochin China. Large quantities of this oil are now exported from 
China to this country and America for use in the paint and varnish industries. 

The best grades of wood oil are shipped from Hankow and are sold as Hankow 
wood oil. 

The Japanese wood oil is not considered to be equal to the Chinese. 


Extraction of the Oul 


The methods in vogue are still very primitive. The cold pressed oil, which 
is the quality mainly exported, is obtained by the natives by crushing the seeds 
and extracting the oil by means of hand presses. 

Sometimes the seeds are roasted over fires and ground between stones before 
expression ; when this procedure is adopted a greater yield is obtained. 

The seeds contain about 50 per cent. of oil. The oil cake is poisonous, and 
hence can only be used as a fertiliser. 

The crude oil is allowed to settle and is then filtered through coarse sacks 
and sold to the Chinese merchants, who export it to Europe, no chemical refining 
being necessary. 


Chemical Composition 


Wood oil contains a large proportion of the glyceride of oleomargaric acid 
{oleostearic acid C,,H,,COOH), a stereo-isomeride of linolic acid. 


Properties and Uses 


The colour of wood oil varies from a pale yellow to a dark brown, the paler 
oils being more highly esteemed. It has a distinctive odour. 

In its natural state wood oil dries rapidly with a flat, waxy, white surtace, 
which has a frosted appearance. It is used by the Chinese as a natural wood 
varnish for coating the bottoms of their junks to render them waterproof. It 
is also largely used in this country on account of its water-resisting properties in 
the manufacture of boat and yacht varnishes. 

At about 0° C. the oil solidifies to a white waxy mass. On heating the oil to 


188 THE CHEMISTRY OF PAINTS 


293° C. (560° F.) for about ten minutes it polymerises, and is converted into a 
stiff jelly, which can be cut with a knife. 

Iodine dissolved in chloroform and added to 20 per cent. solution of the oil 
in chloroform causes it to solidify rapidly. 

Wood oil is largely used in conjunction with rosin in the preparation of wood 
oil varnishes (see Chapter XVIII.). 

Wood oil fatty acids in combination with lead, cobalt, etc., make excellent 
driers (lead tungate, etc.). 


Average Analytical Constants for Wood Oil 


Specific gravity at 15-5° C. me U-OeE 
Saponification value. : . ile eee a 

Acid value ‘ : . : Rp | 
Unsaponifiable matter . ; .. c=) 0-5 pergent 
Todine value (Wijs) 5 d : Ry hs, 

Refractive index 40° C. (ZB) : ae pees 


Scheme for Analysis of Wood Oils 


The various analytical constants for wood oil are obtained according to the 
methods given under the scheme for analysis of linseed oil. 

A very quick yet satisfactory method for determining the purity of a sample 
of wood oil is the heating or polymerisation test. This may be carried out in the 
following manner :— 

Heat Test.—Place 100 gms. of the oil in an open metal pan 6 inches in 
diameter and heat rapidly to a temperature of 540° F. Keep the oil at about this 
temperature and stir well till it begins to solidify. Note the time required after the 
oil reaches 540° F. till it begins to solidify. This should not exceed 74 minutes 
for any good quality of wood oil. 

When the oil has solidified in the pan turn it out while still hot, and cut with 
a knife. Pure Hankow wood oil gives a pale, firm product, and cuts under the 
knife like dry bread without sticking. 

If the oil requires longer than 74 minutes to solidify after reaching 540° F., 
and the resultant product is dark, soft or sticky, then the oil is adulterated. 

An alternate method consists in filling a large boiling tube nearly three-quarters 
full with the sample, and placing it in an oil bath heated to 293° C. (560° F.) along 
with a similar sized tube containing an equal volume of pure Hankow wood oil. 

The oil bath is maintained at 293° C. for ten minutes. The tubes are then 
removed and the consistency of the jelly-like mass noted. 

A pure oil should give a hard jelly which can be cut quite easily. If the oil 
contains 10 per cent. of, say, soya bean oil or linseed oil the jelly form will be quite 
soft and sticky. 

Specification for Wood Oil 


1. It should be pure Hankow wood oil, pale in colour, bright, and perfectly 
free from any admixture of other oils. 





Hi 


AASUTAMHAA LUGAR 








Fie. 32.—FvuLier’s EartoH Or Rerrmine Prant. (Rose, Downs & Thompson, Ltd.) 


DRYING OILS 189 


2. The specific gravity of the oil at 15-5° C. should be between 941 and 942. 

3. The refractive index of the oil at 40° C. should be about 1-475. 

4. The oil should contain not more than 0-75 per cent. of unsaponifiable 
matter. 

5. On heating a portion of the oil at 540° F. for ten minutes the resultant 
jelly-like mass should be hard and cut cleanly with a knife. 

6. The saponification value of the oil must be not less than 190 nor greater 
than 195, 

7. The iodine value (Wijs method) of the oil should be not less than 160. 


Sova Bean OIL 


Soya bean oil has been used as a substitute for linseed oil when the price of 
the latter, owing to short supply, has risen considerably above that of bean oil. 

The soya bean (Glycine hispida) is native to China, Manchuria and Japan. 
The seeds, which are of the shape and size of a pea, contain about 18 per cent. 
of oil. 

In recent years enormous quantities of the beans have been shipped from 
Manchuria to this country, chiefly to Hull, where the oil is extracted in the Anglo- 
American presses, a yield of about 10 per cent. of oil being obtained. 

The cake after expression forms a valuable cattle food. 

Soya oil is also obtained by extraction with solvents, a greater yield being 
thus obtained. 


Properties and Uses 


Soya bean oil is of a brownish yellow colour, but on refining by sulphuric acid, 
caustic soda, or Fuller’s earth, a pale yellowish oil is obtained. 

The plant (see Fig. 32) for refining soya bean oil (and other oils) with Fuller’s 
earth consists essentially of (a) a vortex mixing kettle for mixing the Fuller’s 
earth with the oil to be treated and (b) a filter press for subsequently removing 
from the oil the Fuller’s earth together with all suspended matter, leaving the oil 
quite clean and bright. 

Soya bean oil has a characteristic sweet odour and taste. It is largely used 
as an edible oil, and for the manufacture of soap. 

As a paint oil it is not very satisfactory alone on account of its poor drying 
properties (iodine value 130); hence it is usually used in conjunction with linseed 
oil. 

The manufacture of boiled soya bean oil from raw bean oil is carried out much 
in the same way as described under boiled linseed oil, but in this case a very much 
larger proportion of driers is necessary in order to produce a satisfactory drying 
oil. As a rule cobalt driers are used as giving more rapid drying properties to 
the bean oil. 

Analysis.—See under Linseed oil. 


190 THE CHEMISTRY OF PAINTS 
Average Analytical Constants for Soya Bean Oil 


Specific gravity at 15-5°C. 4 Siig es HOF) 

Acid value .  . . f : ese eb 
Saponification value. : oh = LOS 

Iodine value (Wijs) : > e130 

Refractive index 40° C. (ZB) ; == 563 
Unsaponifiable  . ; ; : . == 0:5 per cent. 


PERILLA OIL 


This oil owing to its superior drying properties and the hardness of the 
resulting film is finding an increasing use in the manufacture of paints and varnishes. 
The quantity available, however, is not very great, and its comparatively high 
price prevents its more general use. 

It is obtained by expression from the nuts of the Perilla ocumoides, which is 
indigenous to China, Japan and the East Indies. It resembles linseed oil both 
in colour and smell. It is remarkable for its very high iodine value, which is the 
greatest of all known vegetable oils. 


Average Analytical Constants for Perilla Ou 


Specific gravity at 15-5°C. : 7) et a ee 
Acid value . ; : ; : de 
Todine value (Wijs) —.. : t .  ==205 
Saponification value. : ek 
Refractive index at 40°C... ; . =e Sie 


MENHADEN Ott (FisH Ort) 


The fish oil most commonly used in the paint industry (especially in America) 
is the variety obtained from the body of the American fish Alosa menhaden, and is 
usually called menhaden oil. 

The oil is obtained by boiling the fish in water or by a process of steaming. 
On settling, the oil rises to the surface, and is skimmed off. The residual fish remains 
are pressed to extract the remainder of the oil, after which they are dried and sold 
as fertilisers. 

The oil thus obtained is rather brown in colour, and contains a lot of stearine ; 
it requires to be bleached and filtered before use. The bleaching process tends to 
remove the objectionable smell of the oil. 

Menhaden oil when boiled with driers yields a boiled oil which dries well, giving 
tough elastic films, which possess excellent waterproofing qualities. Its strong 
fishy smell prevents its more extended use in the paint industries, although in the 
linoleum trade a considerable quantity is used. 


DRYING OILS 191 


Average Analytical Constants for Menhaden Oil 


Specific gravity at 15-5°C. . 3 5 Ree (USL 
Saponification value . f : : - == 192 

Acid value ; : ; ‘ , cae aD 

Iodine value : : . 4 ==165 
Refractive index 40° C. (Z B) : : Be 2 
Unsaponifiable . == 1 per cent. 


It will be noted that the abe faures ae a Saree similarity to those 
given by linseed oil. 


Hemp SEED OIL 


This oil is obtained from hemp seed (Cannabis sativa) which is cultivated in 
N. America, India and Japan. It has a greenish colour, which darkens with age, 
becoming brown. Occasionally it is used as a substitute for linseed oil, or as an 
addition to linseed oil when the difference in price makes it worth while. 

It is not equal to linseed oil in drying properties, and on account of its colour 
can only be used in making dark coloured varnishes. 


Average Analytical Constants for Hemp Seed Oil 


Specific gravity 155°C. : : se O98 
Saponification value . é : : ., = 190 
Acid value : : ‘ ‘ ; 2 =e 0-75 
Unsaponifiable = 


175 


Todine value (Wijs) 


WaLnout Om 


This oil is obtained from the common walnut (Juglaus regia), which contains 
over 60 per cent. of oil. Cold-pressed oil is commonly produced, which is almost 
colourless and has an agreeable taste, and an odour of walnuts. Hot-pressed oil 
is greenish in colour, with an acrid flavour. 

Cold-pressed oil bleaches quickly in sunlight, and because of its pale colour is 
used as an artists’ oil, and in the preparation of fine varnishes. 


Average Analytical Constants for Walnut Oil 


Specific gravity at 15-5° C. . ! : - == 0926 
Saponification value . : : ‘ fea hs) 

Acid value : : ; ‘ : aoe LTD 
Unsaponifiable . ‘ ; ‘ . = 0-5 per cent. 
Iodine value (Wijs) . : : to 150 
Refractive index 40° C. (Z B) ; ; #221, 60 


Poppy SEED OIL 


This oil is made by pressing the seeds of the poppy (Papaver somniferum), 
which grows in India, Russia and France. The seeds contain 40-50 per cent. of oil. 


192 THE CHEMISTRY OF PAINTS 


Pure “cold drawn” poppy oil is a pale golden yellow colour. Its specific 
gravity is -925, and its iodine value 134. 

It is sun bleached for artists’ use, and is extensively used for the preparation 
of artists’ paints. 


NIGERSEED OIL 


This is obtained from the seeds of G'uizotia oletfera grown in tropical Africa ; 
it is of a pale yellow colour. Its specific gravity is about 0-925, and its iodine value 
(Wijs) about 132. 

When the price allows, it is used as an adulterant of linseed oil, although its 
drying properties are very much less. 


SUNFLOWER OIL 


This oil, which has fairly good drying properties, is expressed from the seeds 
of the common sunflower, which is largely cultivated in Russia, China and India. 
It has a golden yellow colour and is sometimes used as a substitute for linseed oil. 

Its specific gravity is 0-924, and its iodine value (Wijs) about 130. 


LumBane Or (CANDLENUT OIL) 


This oil is obtained from the seeds of Alewrites moluccana, a tree which flourishes 
in the western tropics. 

It has been used in America as a substitute for linseed oil in the manufacture 
of paints, but is not very satisfactory on account of its inferior drying properties, 
and also its tendency to darken on heating. 

Its specific gravity at 15-5° is 0-925 and its iodine value (Wijs) is about 165. 


RusBsBeER SEED Ort (PARA RuBBER TREE SEED OIL) 


This oil is obtained from the seeds of the Para rubber trees (Hevea brasiliensis) 
a native of Brazil. It also has been suggested as a substitute for linseed oil, but on 
account of its very poor drying qualities it is quite useless for this purpose. 

Of a pale yellow colour, its specific gravity is 0-923 and the iodine value about 
115 (Wijs method). 


Corn Ort or Maize OIL 


This oil is obtained from the germ of the Indian Corn (Zea mais). It is a clear 
golden yellow oil with a characteristically pleasant odour and taste. It is used in 
America for adulterating linseed oil, but its drying properties are very weak, and 
its use for this purpose is very unsatisfactory. 

Its specific gravity is 0-925 at 15-5° C., and it has an iodine value of about 119 
(Wijs method). 


DRYING OILS 193 


Rosin Om 


When rosin is distilled in fire-heated stills (Fig. 33) into which superheated 
steam is passed, or even by means of superheated steam alone, five principal products 
are obtained, namely— 


1. Gaseous matter ; . 2-5 per cent. | 150° C 
2. Acid water (acetic and formic acids) . . 25 3 
3. Rosin spirit ; : E : , rod : 200° C. 
4. Rosin oils (pale, blue and green) : . 85 vs 350° C. 
5. Pitch : ; ‘ ; : i nies 


2? 


Rosin oil varies in colour and consistency from a thin fluid to one as thick as 














Fic. 33.—Rostn STILL AND CoNDENSING WoRM. 


syrup. The earlier fractions are the palest in colour, lightest in density, and the 
most mobile. 

The specific gravity varies from 0-92 to 1-030. 

The cruder varieties have a bluish bloom or fluorescence, which becomes less 
marked after careful refining with caustic soda. 

Rosin oils contain varying amounts of free rosin acids, which range from 9 to 
30 per cent. according to the specific gravity of the oil. 

Rosin oil, when exposed to the air, absorbs oxygen, and produces a glossy, hard, 
inelastic film; it is therefore sometimes used as an adulterant of linseed oil, 
especially in the manufacture of the so-called “ boiled paint oils.” Its presence 
is readily detected by the Liebermann-Storch test, and by the percentage of 
unsaponifiable matter. 


CHAPTER XVII 


SOLVENTS AND DILUENTS 


Patnts and varnishes always contain, as one of their essential constituents, 
a proportion of volatile bodies which act as solvents or diluents in order 
to reduce them to a suitable working consistency so that they may be readily 
applied. 

The proportion of these volatile bodies varies considerably according to the 
nature of the medium to be thinned out, and also according to the viscosity 
required of the finished product. 

For example, the proportion of volatile solvents needed to produce paints and 
varnishes suitable for application by spraying or dipping is naturally much greater 
than where these materials are applied by brushing. 

The volatile constituents, in most cases, simply function as solvents or diluents, 
and after the application of the paint or varnish volatilise away, leaving the non- 
volatile constituents behind spread out evenly in the form of a thin film on the 
surface to which they have been applied. 

In certain cases, however—and this is especially noteworthy as regards oil of 
turpentine—the solvent functions not only as a volatile medium, but also as an 
oxidising agent, inasmuch as it absorbs oxygen, whereby the oxidisable non-volatile 
constituents are oxidised more rapidly and completely to hard films; in addition, 
such solvents leave behind a small proportion of resinous material which acts as a 
binding agent. 

The solvents in general use in the paint and varnish industries are very 
numerous, and their number is increasing year by year. 

American turpentine is still by far the most valuable and highly esteemed 
of all the solvents that are in general use in the paint and varnish industries ; 
though of late years, on account of its comparatively high price, it has been 
replaced to a considerable extent by turpentine substitutes consisting of petroleum 
distillates (mineral turpentine). 

These petroleum distillates, although lacking in many of the valuable properties 
of turpentine, nevertheless may be considered to be of great value as solvents ; their 
use increases year by year, and there is little doubt that the time will come when 
the natural supplies of turpentine will become so reduced that it will be completely 
replaced by these substitutes. 


194 


SOLVENTS AND DILUENTS 195 


TURPENTINE 


(Spirits of Turpentine, Oil of Turpentine, American Turpentine, 
“ Turps,” Oleum Terebinthine.) 


Turpentine, Gum Turpentine, Oil of Turpentine, and Spirits of Turpentine is 
the name variously given to a product which has long been used in the paint and 
varnish industries. It is obtained by the distillation of a concrete oleo-resin which 
exudes from various species of trees belonging to the Conifer. 

The greater part of the American turpentine is obtained from the southern 
long yellow leaf pine (Pinus palustris). Approximately 75 per cent. of the world’s 
supply of turpentine is produced in the United States, the remaining 25 per cent. 
being mostly obtained in the coastal regions of south-western France from the 
maritime or cluster pine (Pinus pinaster or maritima). 

Small quantities of turpentine are also obtained in Spain and Portugal 
from the Spanish pine; in Greece and Algeria from the Aleppo pine (Pinus 
halepensis) ; in Northern India from the chir pine (Pinus longifolia) ; in Central 
Germany, Poland and Northern Russia from the Norwegian pine or Scotch fir 
(Pinus sylvestris). 

The method used to secure the exuding concrete oleo-resin is to “ box” the 
trees during the winter months by making incisions in the trunks of the coniferous 
trees about 1 to 2 ft. from the ground, so as to form a cavity into which the 
resinous exudation known as “gum thus” can flow. Hach of these cavities or 
“boxes” has a capacity of about three pints, and sometimes as many as three 
“boxes” will be made in one tree. The trunk above the “ box” is cut in several 
places in order to assist the flow. About March the sap begins to run and collect in 
the “ boxes,” and continues during the whole of the summer months. 

The gum is collected from the boxes, emptied into barrels, and conveyed to the 
stills. 

The method of distillation is practically the same to-day as it was fifty or 
sixty years ago. The apparatus consists of a large copper kettle of 500 to 1000 
gallons capacity, connected by a removable still-head to a copper worm kept cool 
in a large tub of water. The stills are, as a rule, fire-heated, though sometimes 
superheated steam is now used. 

From seven to fourteen barrels of gum are distilled at one operation. Water 
comes over with the turpentine at first ; and afterwards a small stream of water is 
allowed to run into the still so that the turpentine distils off at a temperature lower 
than its boiling-point in a current of steam. The water and turpentine pass together 
into the receiver, and are separated and removed at different levels by suitably 
inserted pipes. 

The yield of turpentine is about 25 per cent. of the charge, whilst the residue 
in the still consists of the rosin (colophony) of commerce. The latter is usually 
paler in colour when superheated steam is used in place of direct fire heat. The 
colour of the rosin residue is, however, also dependent on the nature and quality of 
the oleo-resinous exudation that is being distilled. 


196 THE CHEMISTRY OF PAINTS 


Properties and Uses 


Turpentine, or “ Turps,” is a clear, water-white mobile liquid having a 
characteristic odour and taste. 

Its specific gravity is 0-862 to 0-870 at 15-5° C. It boils at about 160° C. 
(320° F.) and almost entirely distils below 180° C. (356° F.), little or no residue 
remaining. 

Turpentine is an essential oil, and consists almost entirely of the Terpene 
“Pinene,” a hydrocarbon of the formula C,)H,,, which 
exists In two modifications « and 8 (it contains 72 per 
cent. « and 28 per cent 8 Pinene). American turpentine 
is dextro-rotary (+1° to +15°). In the presence of air 
it absorbs oxygen and becomes viscous; the oxygen 
so absorbed is readily transferred to other substances, 
so that this liquid, as has already been mentioned, 
acts In varnishes and paints not only as a solvent but 
also as an oxidising agent. Petroleum distillates, on 
the other hand, are inert, and do not act as oxidising 
agents, but promote the drying of paints and varnishes 
only by their greater or less volatility. 

Turpentine is inflammable and burns with a smoky 
flame. It flashes at 94° F. It is soluble in its own 
volume of glacial acid, in ether, benzol, etc. 

It is a good solvent for oils, resins and waxes, 
hence is largely used in the paint and varnish industries 
and in the manufacture of shoe polishes. 























































































































































































































Average Analytical Constants for American Turpentine 















































Specific gravity at 15-5°C. . = 0-864 

Flash point (Abel) : . (=e 

Refractive index at 15:5°C. . = 1-468-1-478 
igs Ate he eras Todine value (Wijs) . =400 

Boiling-point : : - &100a%. 


SCHEME FOR THE ANALYSIS OF O1L OF TURPENTINE 
1. Specific Gravity 


The specific gravity is determined at 15-5° C. in a 50 cc. gravity bottle (see 
Chapter XVI). 


2. Refractive Index 


The determination is made at any convenient temperature with an accurate 
instrument, and the results calculated to 15-5° C., using the correction -00042 for 
each degree that the temperature of determination differs from 15-5° C., 





SOLVENTS AND DILUENTS 197 


3. Flash Point 


The flash point of an oil or spirit is that temperature at which sufficient vapour is 
evolved to form with the air in contact with it an inflammable or explosive mixture. 
In the case of turpentine and those spirits which flash below 120° F. the determination 
is usually carried out in the standard Abel Flash Point Apparatus (Close test) 
(see Fig. 34). This apparatus consists of a metal cup of standard size provided 
with a gauge and a closely-fitting metal cover. The metal cover is fitted with a 
thermometer which dips in the liquid under test, and also a movable slide by which 
the cup can be opened or closed at will. 





4 





se ee ot re ee 
-------4 






Bt 


\ 
\ 
T 
| 
NL 
4 


Fig. 35.—StTANDARD DISTILLATION APPARATUS. 


A small gas jet fixed on a pivot is made to dip into the opening at each degree 
rise of temperature, the action of opening the slide causing the flame to be applied. 

The cup is heated by means of a bath of hot water at 130° F., and is filled with 
turpentine just up to the level of the gauge and the lid carefully pressed into 
position. 

The small jet of gas is lit, and when the temperature reaches about 68° F. the 
slide is opened, which motion causes the jet to dip into the chamber. 

The slide is opened and closed for each degree rise of temperature. The flash 
point is that temperature at which a large blue flame appears, and which spreads 
over the whole surface of the liquid and usually extinguishes the flame. A 
correction is necessary for atmospheric pressure, as the temperature of the flash 
varies 1-6° F. for each inch of the barometer. 


198 THE CHEMISTRY OF PAINTS 


4, Iodine Value 


The iodine absorption of turpentine is carried out by the Wijs method in 
the manner described in the determination of the iodine value of linseed oil 
(Chapter XVI.). 

Care should be taken to have an excess of 100 per cent. of iodine, and it is usual 
to perform the test side by side with a control specimen of pure turpentine. 


5. Distillation Test 


The most satisfactory test for ascertaining the purity of turpentine is to distil 
fractionally 100 c.c. in a standard Engler 
flask connected with a long condenser 
(see Fig. 35) and a graduated 100 c.c. 
recelving cylinder. 

The distillation is performed as 
follows :—Carefully measure out 100 c.c. 
of the sample of turpentine in the 100 
c.c. receiving cylinder and pour into the 
+ standard Engler flask (Fig. 36). Insert 
1 the cork provided with an accurate 
thermometer graduated from 0 to 400° C. 
at intervals of 1° C. and the marks 
numbered at every interval of 10° C. 

The flask is connected with a glass 
condenser 60 cm. in length. The measur- 
ing cylinder may be used without drying 
as the receiving vessel for the distillate. 

The flask is heated directly with a 
| small Bunsen flame, which is carefully 
| surrounded with an asbestos shield as a 
pe CIC as protection from draughts. The heat 

Fic. 36.—SranDarD EnGuer DISTILLATION should be so regulated that the distilla- 
FiasK. tion proceeds at the rate of 5 c.c. per 
minute into the receiving cylinder. 

The temperature at which the first drop leaves the lower end of the condenser 
is considered the initial boiling-point. Readings of the quantity in the receiver 
are taken when the next 10° point is reached, and for every 10° thereafter. 

The distillation is continued until the point is reached where the last drop is 
vaporised and the bottom of the flask is dry. 

If desired the various fractions may be kept separate and ‘there specific 
gravity and refractive index taken. 

Distillation in Steam.—Another method of conducting the distillation is to use 
steam, and thus altogether avoid direct heating. By this method any chance of 
the decomposition of the heavier fractions is avoided. 






ee ear ee CRN ee 


bah al eee 






100cc.Leve/ \ 









SOLVENTS AND DILUENTS 199 


6. Polymerisation 


(a) Take 20 c.c. of concentrated sulphuric acid in a graduated narrow neck 
flask. Cool and slowly run in drop by drop 5 c.c. of the turpentine to be tested 
with shaking. 

Great care must be taken that the temperature of the mixture does not rise 
above 60° C. 

After half an hour warm on a water bath to about 70° C., shaking well at 
intervals. 

Cool to room temperature and add concentrated sulphuric acid till the 
unpolymerised portion rises into the graduated neck. Read the amount of the 
unpolymerised portion ; separate and note its odour, colour, etc. 

(b) Oxidation by Fuming Nitric Acid.—Put 30 c.c. of fuming nitric acid in a 
100 c.c. flask and cool in a freezing mixture. Add 10 .c. of the sample of turpentine 
from a burette drop by drop with continuous agitation. When the reaction is over 
pour into a graduated cylinder and read off the volume of the unattacked portion. 

American turpentine as shipped from the States is hardly ever adulterated, 
and although the author has tested many thousands of such deliveries he has never 
been able to detect any of the various adulterants, such as petroleum distillates, 
benzoles, rosin spirit, chlorinated hydrocarbons, etc., which figure so largely in the 
various text-books dealing with this subject. 

In some cases no doubt the true gum turpentine or spirits of turpentine may be 
mixed with a proportion of wood turpentine (see overleaf), but as this product, when 
carefully prepared, has the same chemical and physical constants as the genuine 
article distilled from the oleo-resin, its detection by the usual analytical methods 
is impossible. If present, however, in a greater proportion than 10 per cent. its 
presence is readily indicated by its peculiar woody empyreumatic odour. 


Specification for American Oil of Turpentine 


(1) The turpentine must be a volatile oil distilled from the resinous exudation 
of the live pine (Pinus palustris and other species of pine) unmixed with any other 
substance such as wood turpentine, petroleum distillates, etc. It must be clear 
and colourless, and free from water and sediment, and possess a characteristic odour. 

(2) Three drops allowed to fall on a piece of white filter paper must completely 
evaporate at a temperature of 70° F. without leaving a stain. 

(3) When 100 c.c. of the material are distilled from a standard Engler flask of 
100 c.c. capacity, under a pressure of 760 mm. of mercury, and at the rate of not 
less than 3 c.c. nor more than 4 c.c. per minute, not less than 70 c.c. should distil 
at or below 160° C., and not less than 90 c.c. at or below 170° C. 

(4) The Baeettie gravity of the material at 15-5° C. must not be less than 0-862 
nor greater than 0-872. 

(5) The flash point (close test) must not be below 90° nor above 100° F. 

(6) When 10 gms. of the turpentine, contained in an open dish, is maintained 

re) 


200 THE CHEMISTRY OF PAINTS 


at a temperature of 212° F. for two to three hours, the residue must not exceed 
2 per cent. 

(7) The refractive index shall not be less than 1:46 nor more than 1-478 at 
15-5° C. 

A typical sample of genuine American turpentine tested by the author gave 
the following results :— 


Specific gravity at 15-5°C. . : ; : : : 0-864 

Flash point (Close test) : : : : : ee OE 

Refractive index at 15-5° C. . : ‘ ; J : 1-470 

Commences to distil at : : , ‘ : . 156-5° GC: (BP) 
160° C. : ; ; : . 5:4 per cent. 
170° C. : . 94-0 A 
180° C. : e . 98-0 is 
190° C. 1999-0 _ 
200. , : : : . all over 
Residue. : ; : . nab 


Woop TURPENTINE 


The growing scarcity of genuine gum turpentine has caused the American 
producers to turn their attention to the manufacture of turpentine from the resinous 
wood of pine trees. This product is known as “ wood ” turpentine. 

Wood turpentine may be extracted with volatile solvents, by steam, or by 
destructive distillation. 

The manufacturers of wood turpentine now produce a product that comes 
within the accepted physical and chemical limits of gum turpentine, though the 
smell of this product may be readily distinguished from that of the characteristic 
smell of genuine gum turpentine. 

Wood turpentine is as a rule obtained by two methods. The usual process is 
by the destructive distillation of the branches or the roots of the pine or mill waste 
whereby the turpentine thus obtained has an empyreumatic or pungent woody 
odour, due to the decomposition products from the breaking down of the rosin and 
the wood which renders the refining of the turpentine a difficult matter. 

The other process of obtaining wood turpentine is by the steam distillation of 
the chipped stumps or mill waste whereby any serious decomposition of the wood 
or rosin is avoided. On redistillation the wood turpentine thus procured has a 
pleasant odour suggestive of pine wood ; and the constants come within the accepted 
physical and chemical limits of gum turpentine. 


Analysis 


The valuation of a wood turpentine is carried out in exactly the same manner 
as already described under the analysis of gum turpentine. If the product possesses 
a nasty pungent woody smell, and contains over 10 per cent. of heavier fractions 
(pine oils) it should be rejected as being unsuitable. 


SOLVENTS AND DILUENTS 201 


A typical sample of a genuine crude wood turpentine on analysis gave the 
following results :— 


Specific gravity at 15-5°C. . : . : : 0-867 

Flash point (Close test) : : : : : wero: 

Commences to distil at : : : , : wb loos 
160° C. é : ; ‘ . 8 per cent. 
170° GC, : : : i ao 
180° C. : ! : : Pais 43 
190° C. ‘ ' , ; MeO us, 
200° C. : : ‘ : oe aC Pie 2 
210° C. ‘ ; : : eee OG? ovis 
Residue. ; : ; ; eae 


FRENcH TURPENTINE 


This variety is obtained by the distillation of the resinous exudation from the 
maritime pine (Pinus marituma, Pinus pinaster) which grows extensively in the 
South-West of France. 

The process in use is very similar to that in America and need not therefore be 
described in detail. 

Properties and Uses.—The properties of French turpentine are very similar to 
those of American turpentine, and it may be used in every case in place of the latter 
product. 

French turpentine is levo-rotatory (—18 to —40) whereas the American variety 
is dextro-rotatory. 

It consists almost entirely of the Terpene “ Pinene” (C,,H,,) containing about 
63 per cent. a Pinene and 37 per cent. 8 Pinene. 

It may be readily distinguished from American gum turpentine by its 
characteristic sweet smell. 

The great bulk of the French turpentine is consumed in France, and only a 
small proportion is shipped to this country. 


Russian TURPENTINE (SWEDISH TURPENTINE) 


Russian turpentine is obtained by the distillation of the wood from the 
Norwegian pine or Scotch fir (Pinus sylvestris). 

It consists mainly of the terpenes cinene and sylvestrine; hydrocarbons of 
the formula C,,H,,, and only a very small quantity of pinene. Russian turpentine 
is dextro-rotatory. It resembles American in many of its properties ; it 1s, however, 
more variable in its composition and has a greater range of distilling temperature. 

It is noteworthy on account of its characteristic nasty odour, which produces 


nausea and headaches, and renders it quite unsuitable for use in paints and varnishes. 


Deodorisation of Russian Turpentine 
Owing to its rank unpleasant smell many patents have been taken out for its 
deodorisation. The usual process, on the commercial scale, is as follows :— 


202 THE CHEMISTRY OF PAINTS 


The crude turpentine is churned in revolving wooden barrels for eight hours 
with about 5 per cent. of concentrated sulphuric acid. A considerable residue of 
black tarry matter separates out after this operation, and is drawn off. 

The treated turpentine is next churned for three hours with a strong solution 
of caustic soda to remove all traces of acid. The turpentine is then pumped into 
stills and distilled over in the presence of caustic soda by means of superheated 
steam. 

Another process consists in distilling the crude Russian turpentine in the 
presence of about 4 per cent. of metallic sodium by the aid of superheated steam. 

In both cases a thick resinous mass is left behind in the still. 

The pure oil of turpentine thus obtained has a characteristic fairly sweet 
pleasant odour, but, unfortunately, no process has as yet been discovered whereby 
the crude Russian turpentine can be permanently sweetened to such a degree that 
it can be used in place of American or French turpentine. 

The examination of a genuine Russian turpentine by the author gave the 
following results :— 


Specific gravity at 15-5°C. . : : : : ; 0-864 

Flash point (Close test) : ; : : ; . ) See 

Commences to distil at ; 3 : . 154°C. (BP) 
160° C. ; ‘ ; ‘ 2 per cent. 
170° C. : ; : : See He 
180° C. : : : : - . 
190° C. ; : ae o 
200° C. : : ; «3 - 
Residue. é : : : 2 e 


A sample of Swedish sulphite turpentine gave the following figures on 
examination :— 


Specific gravity . : : , : ; 0-862 
Optical rotation . : 2 ; : : T° 30 
Refractive index : : : . ; 1-4750 to 20° 
Boiling point. : 5 : ‘ : Saas 
Distils between 160-170 < ; ; ; . 66 per cent. 

a nt LTOr1EO?  s, , ; i 2 

» above 1807s Wig ; : F ; ; 6 * 


PORTUGUESE TURPENTINE 


Small quantities of turpentine are obtained from Spain and Portugal from the 
Spanish pine in a similar manner to French turpentine. Shipments of this product 
are occasionally made to this country ; but the bulk is used for home consumption. 

Portuguese turpentine is very similar in its properties to French and American 
turpentine, and may be used in their place. 


oa 


SOLVENTS AND DILUENTS 203 


A typical sample of Portuguese turpentine on analysis by the author gave the 
following results :— 


Specific gravity at 15-5°C. . : : : 0-864 

Flash point (Close test) 2 ; : : ; on OAT. 

First dropat ets : ‘ ; ; . 155° 0. 
160°C... : : ’ . 48 per cent. 
uC) ad be : : ; a) ere 
180" C) : : ; : ; ene Gre. 
NV a8 § Es ; : ; : Ye) =, 
200° C. . 4 ‘ ‘ Bon bg 
Residue . é ; : x oni 


** REGENERATED ” TURPENTINE 


This is a product of synthetic camphor manufacture. It has a peculiar camphor- 
like smell and is sometimes used as a solvent in place of turpentine. Its boiling 
point, 170° C., is considerably higher than that of turpentine. 


TEREBENE (Terebenum). 


This body is a mixture of dipentene and other hydrocarbons obtained by 
agitating oil of turpentine with successive quantities of sulphuric acid until it no 
longer rotates the plane of a ray of polarised light, and then distilling in a current 
of steam. 

It is a colourless liquid having an agreeable odour and an aromatic taste 
(Sp. Gr. 0-862 to 0-866). It does not rotate the flame of a ray of polarised light, 
and should distil between 312-8° F. and 356° F. (156° C.-180° C.), leaving only a 
slight viscid residue (absence of resin). 

Not more than 15 per cent. should distil below 329° F. (165° C.). This body 
should not be confused with terebine, which is a liquid drier (see Chapter XX.). 


TURPENTINE SUBSTITUTES 
(Petroleum Distillates, White Spirit, Benzine, Mineral Turpentine.) 


The rapid depletion of the turpentine forests and the consequent high price 
of turpentine has resulted in the paint and varnish manufacturers making use of 
cheaper volatile solvents which are capable of replacing entirely, or in part, the 
turpentine they used. 

The chief substitute for turpentine is a distillate of petroleum, commonly 
known as “ white spirit” (benzine in America), enormous quantities of which are 
now used in the paint and varnish industries. 

Great controversy has arisen as to the respective merits of these petroleum 
distillates as compared with turpentine, some manufacturers of white spirit claiming 
that their product is equal in all respects to that of turpentine, and capable of 


204 THE CHEMISTRY OF PAINTS 


replacing this body as a solvent for all purposes for which it is commonly used 
in the manufacture of paints and varnishes. 

This view, in the opinion of the author, is quite erroneous, as turpentine is 
by far the best solvent for all oleo-resins, and, as has already been mentioned, it 
is not only superior as regards its solvent properties, but in addition it increases 
the speed of drying of the paint and varnish with which it is mixed both by 
evaporation and by oxidation, and also acts as a bleaching agent on the oil, 
rendering the paint and varnish on drying whiter and paler in colour. 

Moreover, paints and varnishes made with turpentine and applied to bare 
wood are, owing to their superior solvent properties, able to penetrate the more 
or less resinous surface of the wood better than in those cases where white spirit 
is used; thus producing a flat or semi-flat surface on which the succeeding coat 
of paint or varnish can “key” on without showing any tendency to peel, run, 
or shell off (“ Sissing ” of Varnishes, see Chapter XVIII). 

Varnishes made on turpentine and tanked, body up and come to maturity 
much more quickly than those made with white spirit; the gloss also of these 
varnishes is much superior and does not show the objectionable tendency to 
“bloom” or go flat which so often happens in the case of varnishes made on 
white spirit. 

For these reasons it is more satisfactory when white spirit is used to mix it 
with about 25 per cent. of genuine turpentine in order to obtain the best results. 


MANUFACTURE OF WHITE SPIRIT 


The crude material from which white spirit is obtained is petroleum or rock 
oil. The distribution of petroleum is world-wide. The chief areas worked at 
the present day are America (Pennsylvania, California, Mexico, etc.) Hurope 
(Russia, Roumania, etc.) and Asia (Burmah, Borneo, Persia, Java, etc.). 

When petroleum is distilled three main products are obtained, viz.: (1) light 
oils, (2) burning oils, (3) lubricating oils. 

In addition to these oils two other valuable by-products are obtained, viz. : 
vaseline or petroleum jelly and petroleum pitch. 


AMERICAN PETROLEUM 


The petroleum which gushes out from the oil wells of America after boring 
operations is a very crude material, and varies considerably according to the locality 
from which it is obtained. It is subjected to a distillation process whereby the 
various fractions are separated, and the products thus collected are refined by 
treatment either with sulphuric acid and then with caustic soda, or else by means 
of Fuller's earth, bauxite or other processes, for details of which the reader is 
referred to special treatises dealing with the subject, which is outside the scope of 
this book (see Bibliography). 

American petroleum on distillation yields the following products. 


SOLVENTS AND DILUENTS 205 


(1) Light Oils (B.P. 0° C.-150° C.) 


B.Pt. 
(a) Cymogene ; 0° C. 
(b) Rhigolene : : ; ; ‘ : 183° C. 
(c) Benzine . ; : : ; : : 45-60° C. 
(d) Petroleum ether ‘ ; ; ; 70-90° C. 
(e) Ligroin . : ; : : : 120-130° C. 
(f) Petrol, gasoline and benzoline . 70-120° C. 
(g) Naphtha , : : 90-130° C. 


(2) Burning Otls—Kerosene 


Kerosene, or lamp oil, boils at from 150°-300° C. As a rule it is a colourless 
liquid possessing a peculiar smell, which varies enormously according to the refining 
process which it has undergone. Its specific gravity is about 0-820 and its flash 
point varies from 90° F.-120° F. 


(3) Lubricating Oils 


The distillation products of the crude petroleums obtained in Russia, Roumania, 
Borneo and Java may also be sub-divided into three main groups in a similar manner 
to those of American petroleum, although the yields and composition of the various 
fractions of course varies considerably according to the locality from which the 
crude oil is obtained. 

WHITE SPIRIT 


The starting point in the manufacture of white spirit is a petroleum fraction 
which is intermediate between the light oils and the burning oils. 

This distillate has, as a rule, a specific gravity from about 0-798 to 0-811, and 
flashes at a temperature roughly between 74° F. to 95° F. This petroleum fraction 
is pumped into large copper or iron stills heated by superheated steam or sometimes 
by direct fire heat, though in this case the distillate obtained is not so sweet as in 
the case where superheated steam is employed. 

The stills are provided with dephlegmators in order to get a better or more 
even separation of the fractions, and the distillation is conducted, as a rule, under 
reduced pressure. 

As the distillation proceeds more crude petroleum is sucked into the stills to 
replace the portion that has distilled over. The first portions that distil over are 
the lighter fractions, «7hich are put to one side to be used as motor spirit. 

The fractions distilling over between 150° C. and 250° C. are collected, bulked 
together, and again redistilled, while the residue in the still is used as fuel oil. 

The petroleum fraction which has been bulked together and subjected to a 
redistillation process is usually separated into three fractions, viz., light, medium, 
and heavy white spirit, and is put on the market under the general name of white 
spirit, the paint and varnish manufacturer selecting the particular grade that best 
suits his requirements. 


x 


206 THE CHEMISTRY OF PAINTS 


The white spirits thus obtained vary very considerably as regards the sweetness 
of their odour, and as this is a factor of great importance when used as a turpentine 
substitute it is necessary in the case of those spirits which have a pungent unpleasant 
odour to deodorise them. Many deodorising processes are in use, such as the 
treatment with solutions of hypochlorite of soda, bleaching powder, Fuller’s earth, 
and so on. 

The smell is, as a rule, due to the presence of sulphur compounds and varies 
enormously according to the crude petroleum which has been used; the Roumanian 
crude petroleums yielding white spirits having a distinctly pleasant sweet smell, 
while those obtained from the crude petroleum from Ohio and Texas are distinctly 
objectionable. 

Properties and Uses.—White spirit, used as a turpentine substitute, should be 
a colourless mobile liquid having a pleasant odour. It should be free from grease, 
and on evaporation on a water bath at 100° C. should leave no residue. 

Its specific gravity should be about 0-800 and its flash point should be not less 
than 79° F. nor more than 97° F. It should distil between 150° C. and 250° C. 
The iodine value as distinct from that of turpentine is very small. 

White spirit differs in composition according to the petroleum from which it is 
derived, and as it is a solvent composed of a large number of compounds, such as 
paraffin, olefine, and benzine hydrocarbons, the members of which so closely 
resemble each other in their chemical and physical properties, the simplest method 
of securing an approximate separation is by means of distillation. 

At the present time white spirit is used in enormous quantities as a solvent 
or thinner in the paint and varnish industries ; it is used also as a solvent in polishes, 
and as a cleaning spirit. 


Scheme for the Analysis of White Spirit 


In the selection of a white spirit for use as a substitute for turpentine, it is 
necessary to test carefully the various spirits offered as regards their odour, and 
to select only those that have a pleasant and sweet smell and are free from any 
objectionable paraffin or crude petroleum-like odour. 

The spirit must be water-white in colour, and free from any yellowish cast or 
sign of a bloom. 

Solvent Strength—The solvent strength of white spirit varies considerably, 
and as a general rule the heavier fractions show greater solvent properties than the 
lighter ones. 

The solvent strength may be determined by dissolving 10 parts of mixed fused 
calcium lead resinate in 90 parts of the various samples of white spirits, and standing 
the solution in ice cold water along with a standard 10 per cent. solution of calcium 
lead resinate in turpentine. 

Those samples that separate after thirty-six ee should be rejected as being 
deficient in solvent power. 

The gravity, flash point, and distillation figures are obtained in a similar way 
to what we have described under turpentine (see pp. 196-198). 


SOLVENTS AND DILUENTS 207 


Volatility Test.—To test the quickness of drying of a spirit and its freedom 
from grease, three drops should be poured on to a piece of filter paper and the time 
noted for it to completely evaporate as compared with the standard sample. 

No greasy stain should be apparent on the paper after the complete evaporation 
of the spirit. 

Distillation Test.—This test is carried out in the Standard Engler Distillation 
Apparatus in precisely the same way as in the case of turpentine (see page 198). 


Specification for White Spirit 


(1) The white spirit must consist wholly of a distillate of petroleum, water 
white, neutral, clear and free from water. It must be sweet and free from any 
objectionable odour. 

(2) It must not flash (Close test) below 79° F. and not above 97° F. 

(3) The specific gravity of the spirit at 15-5° C. shall be about 0-800. 

(4) When 10 c.c. of the material are put in a glass crystallising dish 23 in. 
in diameter and placed in a steam bath for 24 hours the residue must not exceed 
0-2 per cent. by weight. 

(5) When 100 c.c. are distilled from a standard Engler flask of 100 c.c. capacity 
under a pressure of 760 mm. of mercury, the first drop must issue from the condenser 
at a temperature not below 140° C., and 99 per cent. must distil below 220° C. 

The following distillation figures obtained by the author for various commercial 
white spirits used as turpentine substitutes will indicate clearly the composition 
of such bodies :-— 


No. 1 Grade, No. 2 Grade, No. 3 Grade, No. 4 Grade, 


White Spirit. Light. Heavy. Extra Heavy. 

Specific Gravity at 155°C. . 0-8006 0-786 0-809 0-813 
Flash point (Close test) . Pet Rea iD EG 96°F. 141° F. 
Boiling point (Ist drop over) . 145° C. 130° C. 160° C. 184° C. 

150°C. . : : . Sp.cent. 7 p.cent. xh se 

160°C. . ; , ELVA ap 3; iy 

170° C.. . , F it ee 5S. 5 p. cent. 

eo" C. . ; ; eel btee, Liew ss 65 (Cs; se 

160° GC... 3 2 it ae wah rat Mae To cur. 6 p. cent. 

200° C. . ‘ ; ste eA aire J) emer Shee Shire 

210°C. . : , ao ee: COs, OC aces 2c 

220° C. . : : UU ay, Lee i G25 4s 

230° C. . : : : a ik io oN SE 

240° C. . ; ‘ : bey iy a fe le 

250° C. . ; : : € BY ae O64 45 

Residue . F ‘ : 7 oy b oe ey te tan 


1 Standard grade of white spirit used as a turpentine substitute in varnish manufacture. 


208 THE CHEMISTRY OF PAINTS 


The following figures were obtained by the author on distilling a standard 
No. 1 Grade White Spirit mixed with varying percentages of genuine American gum 
turpentine, and are interesting as illustrating the effect produced by such additions 
on the temperature at which the various fractions distil over :— 


A B C D E 
No. 1 Grade A+25% A+50% A+75% Genuine 
ite American American American American 
Spirit. Turpentine. Turpentine. Turpentine. Turpentine. 
Specific gravity at 15-5° C. 0-800 0-816 0-832 0-848 0-864 
Flash point (Close test) . Si Sa: 84° F. ST 94° FB. 
Boiling point 147° C..* 147°C, 147°C. LAT Cae 
Per cent. Per cent. Per cent. Per cent. Per cent, 
150° C, : ; 3 3 3 3 si 
160° C. ; : 32 24 22 28 75 
TCR ee 44. 66 78 89 98 
180° C. : : 76 85 90 94 99 
190° C. : 2 89 92 94 97 dry 
200° C. : : 94 97 98 98 a 
210° C. : : 99 wo 99 99 
215° C. : ; 99°5 100 100 100 
220° C. : : dry 


CAMPHOR OIL 


The volatile oil which is obtained from the camphor laurel (Laurus camphora) 
—which grows principally in Japan—by a process of steam distillation is 
redistilled to separate out all the camphor, and the residual oil is known 
commercially as camphor oil. 

It is a colourless liquid with a camphor and eucalyptus like smell, and burns 
with a bright smoky-like flame. It has a specific gravity of about 0-875 and flashes 
at 97° F. 

A distillation of a sample of heavy camphor oil by the author gave the following 
results :— 


Hm af 3 : ; : t : . 210 per cent. 
220° Cavers : ; : 224 
yi ano é ; : Oe a 
240°C... : : putt i 
we tba ee : ‘ sig ate 3 
Residue. : é ‘ : F : 1 . 


It possesses fairly good solvent properties and is sometimes used as a substitute 
for turpentine. 


AucoHoL (EtHyt ALCOHOL) 


Ethyl alcohol (C,H;OH) is prepared on a technical scale in the spiritous 
fermentation of saccharine juices. Pasteur considered that during fermentation 


SOLVENTS AND DILUENTS 209 


94 to 95 per cent. of the sugar changes to alcohol and carbonic acid, according to 
the following equation :— 


C,H,,0.=C,H,OH+2C0,. 


Fusel oil (chiefly amyl alcohol C;H,,OH), some glycerol C;H,O, (2-5 per cent.) 
and succinic acid C,H,O, (0-6 per cent.) are formed simultaneously, although the 
latter two appear generally towards the end of the fermentation. 

The material used in the preparation of alcohol by means of fermentation are 
saccharine plant juices and starch containing substances such as the seeds of 
grain and potatoes. 


Manufacture of Potato Spirit 


The potatoes are heated with steam to 140-150° C. under pressure of from 
2-3 atmospheres, and the potato mash thus formed is digested at 57-60° C. in a 
mashing apparatus with finely divided malt containing water. In this manner 
the starch of the potatoes is converted into sugar. The mash is then run into 
fermentation tubs, where it comes in contact with “ pure culture ” artificial yeast 
and is then fermented. Crude spirit results from the distillation of the fermented 
mass. 


Manufacture of Pure Absolute Alcohol 


To purify further the crude spirit it is fractionated in a special column dis- 
tillation apparatus whereby a spirit containing 95 per cent. of alcohol is obtained. 
The last fractions or “tailings” which come over contain large quantities of 
fusel oil. 

To prepare anhydrous alcohol the rectified spirit (90-95 per cent. alcohol) is 
_ distilled and redistilled with ignited quicklime till all traces of water are removed. 


RECTIFIED SPIRITS OF WINE 
(Spiritus Vinus Rectificatus.) 


The alcohol ordinarily met with in commerce is known as “ rectified spirits of 
wine” or “rectified spirit.” It contains 90 parts by volume of alcohol and 10 parts 
by volume of water. Its specific gravity is 0-8337 at 15-6° C. 


METHYLATED SPIRITS 


Mineralised methylated spirits sold by licensed retailers for general use (except, 
of course, as a beverage or medicine) is a mixture of 90 parts of rectified spirits of 
wine with not less than 10 parts of approved wood naphtha plus 4 per cent. of 
petroleum; and this mixture, which is thus rendered non-potable, is allowed by 
the Excise authorities to be sold for domestic purposes free of duty. 

Methylated spirit issold at the strength of 64° O.P. (“ over-proof”’) and has 
a specific gravity of 0-8221. It contains 90 per cent. of alcohol. 


210 THE CHEMISTRY OF PAINTS 


INDUSTRIAL SPIRIT 


As this denaturing process renders the alcohol unfit for many industrial 
purposes the Excise authorities allow an “ Industrial” spirit to be used under 
special regulations ; this consists of a mixture of 95 per cent. rectified spirits of 
wine and 5 per cent. of approved wood naphtha. 

Properties and Uses.—Pure alcohol is a mobile colourless liquid with an 
agreeable characteristic odour. Its specific gravity at 15-5° C. is 0-7939; boiling 
point 78-3° C. It burns with a pale blue flame, which is scarcely luminous. It 
is very hygroscopic and mixes in every proportion with water. The mixture takes 
place with disengagement of heat, and there is a contraction after cooling. The 
maximum contraction is reached when one molecule of alcohol is mixed with three 
molecules of water, corresponding to the formula C,H;OH+3H,0. 

The amount of absolute alcohol in a given sample of commercial alcohol is 
determined from its specific gravity by the aid of a table of percentages, or by 
using specially constructed hydrometers (alcoholometers), which show the percentage 
of alcohol by direct reading. 

Ethyl alcohol forms crystalline compounds with some salts, like calcium 
chloride and magnesium chloride. It plays the part of water of crystallisation in 
them. When subjected to the action of oxidising agents, such as manganese 
peroxide and sulphuric acid, chromic acid and air, it is converted into acetaldehyde 
(CH,COH) and acetic acid (CH,COOH). 

Bleaching powder changes alcohol into chloroform, and iodine and caustic 
potash convert it into iodoform. 

Alcohol dissolves fatty acids and castor oil readily, but it has only a slight 
solvent action on the other fatty oils. It is a first-rate solvent, and readily dissolves 
rosin and other resins such as sandarac, shellac, mastic, etc. It is very extensively 
used in the form of methylated spirits in the manufacture of French polishes and 
Spirit varnishes. 

SYNTHETIC ALCOHOL 


The synthetic production of alcohol from acetylene was largely developed 
in Germany during the war. The acetylene obtained from calcium carbide was 
converted into aldehyde in the presence of a catalyst such as a mercury salt; the 
aldehyde thus formed was reduced to alcohol by passing its vapour, mixed with 
hydrogen, over finely divided nickel at a definite temperature. 

Methylated Finish is methylated spirit containing about 3 ozs. of rosin to 
the gallon. It is chiefly used by French polishers for making up their own polish, 
as the Excise authorities do not place so many restrictions on its sale. 


Metuyt ALCOHOL 
(Wood Alcohol, Wood Naphtha, Wood Spirit.) 


Methyl alcohol CH,OH is obtained by the dry distillation of wood for making 
acetic acid. The crude wood vinegar contains about 3 per cent. of wood spirit, which is 


SOLVENTS AND DILUENTS 211 


removed by neutralising the acid and separating the alcohol by fractional distillation. 
The crude wood spirit thus obtained contains acetone as its chief impurity. 

Methyl acloholis, when pure, a colourless mobile liquid, with a strong characteristic 
smell. It boils at 66-67° C. and has a specific gravity of 0-796. It mixes with water, 
alcohol and ether. It is readily inflammable and burns with a non-luminous flame. 

Wood alcohol is a more powerful solvent than ethyl alcohol and is used to a 
limited extent in the manufacture of spirit varnishes. Owing to its . toxic 
properties care must be taken to see that efficient ventilation is provided wherever 
it is used. 

Amyi Atconot (C,H,CH,OH) 


(Fusel Oil.) 


Fusel oil which is obtained in the distillation “tailings” of alcohol consists 
chiefly of amyl alcohol (isobutyl carbinol). 

It is obtained pure by adding water, redistilling, and collecting the fraction 
boiling at 129-132° C. 

Amy] alcohol is a colourless, mobile liquid possessing a characteristic, unpleasant 
smell; its vapours are very pungent and irritating. 

It rotates the flame of polarisation to the left. Its specific gravity is 0-8184, 
and it boils at 132° C. 

Fusel oil was formerly very extensively used in the manufacture of transparent 
lacquers owing to its excellent solvent properties, but it has been displaced in 
recent years owing to its unpleasant smell and toxic effects. 


Normat Butyt ALCOHOL 
CH,(CH,),CH,OH; B.P. 116° C.; Specific gravity at 20° C. 0-8099 


is now also used as a solvent for spirit varnishes and lacquers on account of its 
excellent solvent properties. 


AcrTonEe (CH,COCHS) 
(Dimethyl Ketone.) 


Acetone is prepared by the distillation of calcium or barium acetate or from 
crude wood spirit. 

It is a mobile, colourless liquid, with a characteristic odour. Its specific 
gravity is 0-814 and boiling point 56-5° C. 

It is miscible with water, alcohol and ether. Acetone is very inflammable, 
and burns with a bright flame. It is an excellent solvent and is very largely used, 
alone or mixed with alcohol and benzol, as a solvent for resins, celluloid, cellulose 
nitrate and acetate (see Dopes, Chapter XIX.). It is also used as one of the 
chief ingredients in patent paint removers. 

Mized Ketones, such as methyl ethyl ketone, methyl propyl ketone, etc., made 
by the distillation of the barium salts of the corresponding acids with barium acetate, 
are also used at the present time as a substitute for acetone in the manufacture 
of dopes and celluloid varnishes. 


212 THE CHEMISTRY OF PAINTS 


ETHER 
(Ethyl Ether (C,H,).0, Sulphuric Ether.) 


Ether is made from ethyl alcohol and sulphuric acid heated to 140° C. The 
process is a continuous one, alcohol being constantly added. 

It can also be made from benzine, sulphuric acid, and alcohol at 135-145° C. 

Anhydrous ether is obtained from ordinary ether by shaking with water to 
remove the alcohol and distilling over quicklime or chloride of calcium, and drying 
it finally with sodium wire until there is no further evolution of hydrogen. 

Ether is a mobile liquid with a characteristic smell, and its specific gravity 
at 0° C. is 0-736. It is an anesthetic. It boils at 35° C., and evaporates very 
rapidly even at medium temperatures. 

It is extremely inflammable, burning with a luminous flame, and its vapour 
mixed with air explodes on ignition. 

It is miscible with alcohol and dissolves in 10 parts of water. Owing to its 
powerful solvent properties it is used as a vehicle for dissolving many organic 
substances. 

CuLorororm (CHCI,) 

Chloroform is prepared technically by treating alcohol or acetone with bleaching 
powder. The bleaching powder is made into a thin paste with water and mixed 
with the acetone. Gentle heat is applied till a reaction sets in, which is indicated 
by the frothing of the liquid. The chloroform distils over, and as the reaction 
subsides heat is applied to complete the distillation. The course of the reaction 
may be expressed by the following equations :— 


1. CH,COCH+3Cl,=CH,COCCI,+3HCL. 
2. 2CH,COCCI,+Ca(OH),—(CH,CO0),Ca-+2CHCI,. 


Chloroform is a colourless liquid of an agreeable ethereal odour and sweetish 
taste. It solidifies in the cold and melts at —62° C. It is readily volatile, and is 
largely used as an anesthetic and also, to a lesser extent, as a solvent for oils 


and waxes. 
CaRBoN BISULPHIDE (CS8,) 


Carbon bisulphide is prepared commercially by passing sulphur vapour over 
red-hot charcoal. In the manufacturing process the charcoal is heated in vertical 
cast-iron retorts set in a suitable furnace. The heat of the furnace also melts the 
sulphur, which is placed near the base of the retorts; the sulphur vapours rise 
through the red-hot charcoal and form carbon bisulphide, which escapes at the 
top. The carbon bisulphide is condensed in 30-ft. long condensing coils. 

The crude product is purified by repeated distillation. 

Carbon bisulphide is a colourless, mobile liquid with a peculiar, offensive smell 
(when absolutely pure its odour is very faint). Its specific gravity at 0° C. is 1-297. 
It is a very volatile and poisonous liquid and readily burns with a blue flame. 

It is an excellent solvent for iodine, sulphur, fatty oils and resins, and is used 
in vulcanising india-rubber. 


SOLVENTS AND DILUENTS 213 


CarBON TETRACHLORIDE (CCl,) 


Carbon tetrachloride is prepared by the action of chlorine on carbon bisulphide. 
It is a pleasant-smelling colourless liquid, boiling at 76° C. Its specific gravity at 
0° C. is 1-631. Owing to its excellent solvent properties it is largely used for 
dissolving oils, fats and resins. It is non-inflammable, and hence can be used in 
place of very highly inflammable and dangerous solvents such as ether acetone and 
carbon bisulphide. 


Amyt Acetate (C;H,,C,H,0,) 


Amyl acetate is obtained by distilling potassium acetate with amyl alcohol 
and sulphuric acid. It is a colourless, mobile liquid having a specific gravity of 
0-896. It has a pleasant pear-like odour, and is chiefly used as a solvent for gun 
cotton in the manufacture of nitro-cellulose varnishes. It boils at 137° C. 

Butyl Acetate, the properties of which closely resemble those of amyl acetate, 
is also frequently used as a solvent for gun cotton in place of amyl acetate. 


Rosin Spirit 


In the distillation of rosin about 10 per cent. of crude rosin spirit is obtained 
(see p. 193), which has a darkish brown colour. 

It is purified by agitation with caustic soda solution and subsequent 
redistillation. 

Rosin spirit is a water-white mobile liquid with a characteristic sharp terpene- 
like odour. Its specific gravity varies from 0-86 to 0-891, and it flashes at about 
100° F. 

In composition rosin spirit is a mixture of several hydrocarbons, such as the 
paraffins, olefines, etc., and varies according to whether it has been obtained by 
steam or fire distillation. 

It boils at about 117° C., and should all distil over below 260° C.; any higher 
boiling point fractions indicate the presence of rosin oil, which is objectionable, as 
it would retard the drying properties of the spirit. 

Rosin spirit is largely used as a solvent, and but for its pungent smell would 
make a good substitute for turpentine. 


SHALE SPIRIT OR SHALE NAPHTHA 


Shale spirit is obtained by the destructive distillation of bituminous shale. 
Large deposits of shale are found in Scotland, and this material is subjected to a 
process of distillation at about 800° F. in large vertical retorts. The chief products 
obtained are :— 

1. Shale Spirit. 8.G. -66--75. 
2. Paraffin Oils. §.G. -76--83. 
3. Lubricating Oils. 

4. Paraffin Wax. 


214 THE CHEMISTRY OF PAINTS 


A proportion of gaseous and tarry matter is also evolved, and a residue of coke is 
left in the still. 

The crude oily fractions that come over contain a lot of tarry matter, and are 
treated first with sulphuric acid and then with caustic soda and again distilled. 

The first fractions that come over constitute the shale spirit or shale naphtha 
of commerce. 

Shale spirit is a water-white mobile liquid having a pungent characteristic 
smell which is rather unpleasant. Its specific gravity varies from -66--75 and it 
boils at about 65° C. Its flash point is about 60° F. 

Shale spirit is a complex mixture, and consists chiefly of paraffins and olefines. 
It is a good solvent and volatilises very quickly ; it is largely used as a thinner for 
quick-drying anti-corrosion paints and in anti-fouling compositions. 


BENZENE, Benzo, Coat Tar NaputHa, SOLVENT NAPHTHA 


In the manufacture of coal gas by the destructive distillation of coal large 
quantities of coal tar are produced, which, when subjected to a process of distillation, 
yield :-— 

1. Light oil (8-5 per cent.). B.P. up to 150°. 

2. Middle oil (8-10 per cent.). B.P. from 150-210°. 

3. Heavy oil (8-10 per cent.). B.P. from 210-270°. 

4, Anthracene oil or green oil (16-20 per cent.). B.P. from 270-400°. 

5. Residue—Pitch. 


The light oils, when subjected to a process of fractional distillation. may be 
separated into the following bodies :— 


Benzol or benzene . : . C,H,. B.P: 81°; 8.G. at 070-899. 
Toluene , ; : » GH BP oie. 
Xylene (o,m,p) . : . C,H, B.P. 138-1419. 


Benzol or Benzene (CgH,) is a colourless liquid with a characteristic smell. 
It burns readily with a luminous smoky flame. It is an excellent solvent, and is 
used in the manufacture of lacquers and dopes and paint removers. 

50 per cent. benzol is a mixture of benzene, toluene and xylene, of which 
50 per cent. distils below 100° C. 

90 per cent. benzol is a mixture of benzene, toluene and xyleie, of which 
90 per cent. distils below 100° C. 

Solvent or Light Coal Tar Naphtha is a mixture of benzene hydrocarbons, and 
is largely used as a solvent in the paint, varnish and india-rubber industries. 

It is a colourless liquid having a peculiar characteristic smell. Its specific 
gravity varies between 0-860 to 0-884, and as a rule 90 per cent. distils below 
170° C. 


BENZINE, PETROLEUM ETHER 


Benzine—which must not be confused with benzene or coal tar benzol (C;H,)— 
is a light petroleum fraction obtained in the distillation of petroleum oil. 


SOLVENTS AND DILUENTS 215 


Its specific gravity is about -638--660, and it boils at from 45-60° C. 

Petroleum ether is a somewhat heavier fraction (B.P. 70-90° C.) and has a 
specific gravity of about -650--660. 

Both bodies are extensively used as solvents for oils, waxes, and in the dry- 
cleaning industry. 


TERPINEOL (C,,OH,,OH) 


Terpineol is obtained when crystalline terpin is boiled with water and 1 per 
cent. of hydrochloric acid, and distilled. It is a colourless oily liquid with a peculiar 
fragrant odour like lilac. It is optically active and boils at 215° C. 

Terpineol is an excellent solvent for medium-hard and soft copals, and only its 
high price prevents its more extended use in the varnish industry. 


EPICHLORHYDRIN (CH,Cl, CH, CH,O) 


Dichlorhydrin is obtained when anhydrous glycerine is mixed with an equal 
volume of glacial acetic acid saturated with hydrochloric acid gas, and distilled. 
When this body is treated with an aqueous solution of caustic potash, and distilled, 
epichlorhydrin is obtained. 

The latter is a colourless mobile liquid with an ethereal smell. It has a specific 
gravity 1-203 at 0° C. and boils at 117°. It is an excellent solvent for all oils 
and resins. 

The following chlorinated hydrocarbons are now extensively used as solvents 
for the extraction of oils from their seeds, and also in the manufacture of varnishes, 
dopes, lacquers and paint removers :— 


C,H,Cl, Dichlorethylene. Sp. Gr. 1-25. Boiling Point 55° C. 


C,HCl, Trichlorethylene. a 1-47. o 872. C. 
C,Cl, Perchlorethylene. i 1-62. se 121° C. 
C,H,Cl, Tetrachlorethane. he 1-60. S 147° C. 
C,HCl, Pentachlorethane. _ 1-70. Hs 159° C. 


CHAPTER XVIII 


MANUFACTURE OF OIL VARNISHES 


THE manufacture of oil varnishes is an industry which at the present time has 
assumed very great importance. Many hundreds of thousands of gallons are 
produced yearly in this country alone, which has long been famed for the excellence 
of its varnishes. In fact, the methods of manufacture used in America and the 
Continent are based on the English practice. 

The varnish made in this country is exported to all parts of the world, and 
is still able, in spite of high tariff restrictions, to compete even in those countries 
which have large manufactories of their own, such as, for example, America and 
France. 

The first known directions for making a linseed oil varnish were indicated 
by a monk named Theophilus so far back as the twelfth century. But for many 
years varnishes were made only in very small quantities by artists for their own 
personal use. 

According to Livache the first varnish factory was started in England in 1790. 
Later, factories using processes based on English methods were established on the 
Continent and in America. 

The composition of oil varnishes is comparatively simple, and consists simply 
of resin, drying oil and a volatile solvent. Nevertheless the manufacture of high- 
class varnish is an art that requires very long experience and an extensive 
knowledge of the various properties of the resins and oils that are necessary to 
produce a high-class product. 

The various proportions in which the gums, or resins, and oils are “ run,” and 
the methods of working them up, together with the amount and character of the 
driers required in the different varnishes that are made, are regarded as valuable 
trade secrets, and consequently very jealously guarded. In many cases the 
processes in use are handed down from father to son, and it is not uncommon to 
find factories where the same family have been employed in the manufacture of 
varnishes over a long period of years. 

Oil varnishes may be roughly divided into the following three classes :— 

(1) Inside Varnishes, which comprise those varnishes which are not durable 
enough to withstand severe outside exposure and weathering influences, and are 
therefore only suitable for indoor use. As a rule they dry off quickly with a hard 
yet brittle, highly lustrous surface or “face.” These varnishes are usually sold 
under the following designations :— 

216 


OIL VARNISHES 217 


Inside copal varnish. Furniture varnish. 
Inside oak varnish. Floor varnish. 


(2) Outside Varnishes, which dry with hard, tough films, and are extremely 
durable, wear well and keep their gloss for a long 
period even under exposure to severe weathering 
influences. The following varnishes are comprised 
under this classification :— 


Durable or finishing body varnish for coach and 
motor work. 

Finishing carriage varnish and hard drying carriage 
varnish. 

Outside oak varnish or elastic oak varnish. 

Coburg varnish, and others. 







































































(3) Stoving Varnishes, which are chiefly used in 


metal work and in the tin-printing trades. tee 7 GAO Cad Rone 


They require to be stoved for a few hours Por; Atumimrom Tor wits 
at a temperature of about 150-250° F., when they 
dry off, giving extremely hard and tough films. 

ee a so: The plant used in the manufacture 
Kk ---7-102 dia. inside --->\ of varnishes is comparatively simple, 


' 


FLANGED-ON DETACHABLE CopP- 
PER OR SPECIAL BRonzE Bottom. 





ee and whilst, of course, modifications 

exist in different factories, and the 
methods of working vary considerably, 
yet in the main essentials the plant 
and processes are the same. 


PLANT AND PROCESSES 


The gums or hard resins are 
carefully selected so that they are of 
uniform size and colour, and in the 
manufacture of pale varnishes any 
dark-coloured resins are carefully 
picked out. The larger lumps of resin 
are put through a resin grinding mill 
or gum crusher to reduce them to 
+ | Jumps of uniform size. 

ey The broken-up gum or mixture 
Bee hin) cits cutside 3 of gums is then weighed out and 
put in a large gum-running pot. 

Pio $iie Starpamy oie Aum The gum pot in which the gums 

or resins are melted (or “run,” as it is 
commonly called in the trade) consists of a large cylindrical copper vessel, 
which is made in two pieces, the bottom part being riveted on to the body of 


OVEall -=a0—--64 S05 


Hw 


, 7, 
See See Ae 


218 THE CHEMISTRY OF PAINTS 


the pot with a flange which is wide enough to overlap the furnace bed, and forms a 
support for the pot, and prevents the flame from going up the sides. 

The bottom part of the pot is subjected to very considerable wear owing to 
being in direct contact 
with the heat, as well as 
to the continuous use of 
stirrers, and requires to 
be renewed from time 
to time. 

The varnish pots— 
known as varnish kettles 
in America—are usually 
made of copper, but some- 


















Fic. 378.—Gum Runnine Pot. DrracHasLe Bottom. 
CovER AND FumME PIPE. 





e=e-= 


= 


aS 


times iron pots are used; and in recent years enamelled 
iron pots have come into favour, especially in the 
manufacture of very pale varnishes. 

Aluminium varnish pots have been used in the 
manufacture of varnishes, and are very suitable for the 
preparation of the very pale varnishes, such as pale 
copal or French-oil varnishes. On account of their 
lightness they are very convenient in use, but un- 
fortunately—so far as the author’s experience goes— 
they are not very durable, and the bottoms are apt 
to fall out after they have been in use for some time. 
This defect renders them, of course, very dangerous. pyg. 38. Varnisn Por Covur 

Aluminium pots are now often made with flanged- = wit Comprnsatine Lirt. 
on detachable copper or special bronze bottoms 
(see Fig. 37). This combined construction affords great strength and resistance, 
so that burning through becomes practically an impossibility, and the life of the pots 
is thereby considerably increased. 

The size of the pots varies considerably, a convenient size being one that has 
a capacity of about 100 gallons. Fig. 374 shows the dimensions of a Standard 


= 









OIL VARNISHES 219 


Aluminium Gum Pot made by the Aluminium Plant and Vessel Co., for “ running ” 
60 Ibs. of gum at one operation. 

The pots are provided with easily movable covers (Figs. 378 and 38), which can 
readily be fixed on during the melting operation, and these are connected by means 
of a pipe with a condensing apparatus where the products of decomposition are 
collected, particular care being taken that the adjustments are made so that none 
of the volatile products that are distilled off can run back into the melting-pot. 

The varnish pot is placed on, but not attached to, a varnish truck provided 
with two wheels, and connected with a long handle to the front axle, and provided 
with an attachment so that the pot may be raised or lowered at will (see Fig. 39). 

By means of the iron varnish truck it is a simple matter to move the varnish 
pots wherever required, and also to raise or lower them to any required height 
from the bed of the furnace during the melting operation (see Fig. 40). 

The top of the furnace is set just below the floor level, and connected with a 
tall chimney to carry off the 
products of combustion. The 
fuel ordinarily used is coke, 
although gas is sometimes 
employed. 

The varnish pot containing 
the requisite amount of gum is 
placed directly over the fire 
and is supported by its flange 
on the bed of the furnace. 
The cover is adjusted and the 
temperature of the gum is 
eradually raised to about 340° 
to 360° C. (650° to 680° F.). 
Should the temperature rise 
too quickly, then the heat 
may be moderated by raising 
the pot a little above the 
furnace bed by means of the adjustable attachment fitted to the varnish truck. 

As the gum melts large amounts of volatile oils are driven off and are collected 
in the condensing chambers. When the gum has lost from about 10 to 25 per cent. 
of its weight—depending on the variety of the gum that is being run—it should 
be perfectly fluid and limpid and run off the stirrers like a thin oil; further, no 
particles of hard or melted gum should be detected when the stirrer is gradually 
worked round the botton of the pot. 

The weight of gum run at a time varies, but as a general rule the charge 
consists either of 50, 100 or 150 Ibs. of gum, though in the manufacture of the paler 
varnishes it is better to run not more than 50 lbs. at one time. 

While the gum is being run, “ prepared” linseed oil is being got ready to 
incorporate with it; and this is usually done by gradually heating up old tanked 





Fic. 39.—VaRnisH Pot CARRIAGE. 


220 THE CHEMISTRY OF PAINTS 


linseed oil—Baltic or refined East Indian oil is the best—to a temperature of 
300° F., then stirring in a suitable proportion of red lead, litharge and manganese 
hydroxide driers, and gradually raising the temperature to about 550° F. 

The hot oil thus prepared is added, in small proportions at a time, to the melted 
resin and vigorously stirred; when the first portion of the oil is in, a sample is put 
on to a piece of bright tin plate and examined to see if it is perfectly transparent. 

The cooled sample on the tin plate must show no signs of white opacity or 
separation. If clear and trans- 
parent it indicates that complete 
amalgamation has taken place 
between the gum and the oil. 
If the mixture is cloudy then 
the heating must be continued 
till a portion taken out is quite 
bright and transparent. More 
oil is then added and again 
tested, and so on till the full 
amount of oil is added. 

The resin and oil mixture is 
then cooked until the varnish, 
when spotted on tin, gives a 
bright transparent product of 
a thick and sticky consistency. 
The pot is then run off the fire 
into the open, and when it has 
cooled down to about 250° F. 


quired viscosity (or “run up”) 
with spirits of turpentine. 

The varnish is then pumped 
while warm through a varnish 
filter press (Hig. 41), the frames 
of which are covered with layers 
of cloth and filter paper. By 
this means all slimy, gummy 
matter, mucilage, and suspended impurities are removed, and the clear varnish is 
then tanked. 

Varnishes may also be rapidly clarified by passing them through a centrifuge 
(see Hig. 42) machine specially designed for this purpose, whereby all the suspended 
matter is eliminated by means of centrifugal force. The machine operates at a 
speed of 17,000 revolutions per minute and thus exerts a separating force 16,950 
times the force of gravity. 

The tank room in which the varnishes are stored is maintained at a temperature 
of about 80-95° F. in order to clear and age them. 





Fig. 42.—SHARPLE’S VARNISH CENTRIFUGE. 


it is thinned down to the re- — 





Fig. 40.—Varnisu Por CarRiaGe witH VaARnisu Pors. 
(Alumini:m Plant & Vessel Co., Ltd.) 





Fic. 41.—Varnisu Fitter Press with SELF-CONTINUED BELT-DRIVEN Pump, 
(S. H. Johnson.) 


’ 


ei 





OIL VARNISHES 221 


Newly-made varnishes are not satisfactory to use, however carefully they may 
be filtered, as they always contain minute particles of matter in suspension, and 
dry with a spotty or ridgy film, which is lacking in lustre. 

The best class of varnishes are always tanked for about six to eighteen months 
before use, and sometimes even as long as two years. During the tanking or ageing 
process the varnishes throw out a sediment, or “foot out” as it is called in the 
trade, and in process of time this sediment or “foot” gradually settles down to 
the bottom of the tank, leaving the varnish above bright and clear. 

In addition to “footing” out, the varnish, during the ageing process, “ bodies ”’ 
or thickens somewhat, and its drying properties are considerably increased, due 
partly to the absorption of oxygen from the air. 

The well-matured varnish is carefully tested before sending out to see that 
it has the right viscosity, and that it dries in the right time with a hard, uniform, 
smooth, glossy, transparent film. 

The above description of the plant and the process used in the manufacture 
of high-grade varnishes is necessarily brief, since the process varies considerably 
according to the particular grades of varnish that are being made. 

Every gum has its own peculiarities as regards its ease of running and the 
amount of oil with which it will satisfactorily amalgamate; and no definite 
directions can be given for the preparation of varnishes, inasmuch as these can 
be learnt only by long experience in the handling of the products. 

Sometimes thickened linseed oil—that is, oil which has been heated until it 
has a high viscosity (commonly known as “ stand oil ”—see page 225)—is used in 
addition to linseed oil: blown oils may also be used. The addition of these 
thickened oils to the melted resin enables the varnish-maker to stiffen up the oil 
resin mass more readily and to a thicker consistency, and he can therefore use more 
turpentine in thinning down. 

Occasionally oleate or linoleate of alumina is added to prepared linseed oil 
to help to body it up, and so to produce the required consistency without so much 
cooking, a process which always tends to darken the finished varnish. 

Again, the nature of the driers employed varies enormously ; some varnish- 
makers prefer to use cobalt acetate or linoleate just before thinning out. Others 
prefer to cook the lead and manganese driers (such as red lead, litharge and 
manganese dioxide) directly into the oil gum mass at a fairly high temperature 
in order to produce quickly a thick stringy medium which will readily take a large 
volume of thinners to reduce it to the right varnish consistency. This method of 
adding the driers is disadvantageous, as it tends to saponify or soap up the varnish, 
with the result that the finished product is very dark and lacks lustre; moreover, 
its wearing properties are apt to be seriously interfered with. 

A better method consists in adding the driers in the form of lead manganese 
resinates or linoleates to the cooked-up mass of gum and oil, and thus prevent any 
chance of saponification taking place; the varnish thus produced is full of lustre 
and is pale in colour. 

In place of turpentine it is customary in the cheaper varnishes to use white 


222 THE CHEMISTRY OF PAINTS 


spirit, or a mixture of turpentine and white spirit, in order to cheapen the cost 
of production. 

The amount of oil required in the manufacture of varnishes varies considerably 
according to the nature of the resins or “ gums” used, and also according to the 
particular purpose for which the varnish is required. 

Varnishes are often classified as “ long oil”’ or “ short oil’ varnishes, depending 
on the amount of oil which has been used in their preparation. 

Varnishes such as French oil varnishes, carriage varnishes, and body varnishes 
are “long oil” types, and contain roughly about 20 gallons of oil to every 100 lbs. 
of gum resin. 

They are tough, durable varnishes, and on account of their elastic and hard 
wearing properties are eminently suitable for outdoor use. 

“Short oil” varnishes, on the other hand, are those which contain only a 
small portion of oil to the gum resin constituent. As a rule they are very hard, 
but somewhat brittle, and are not suitable for hard wearing outside use. These 
varnishes comprise those sold under such names as flatting or rubbing varnishes, 
furniture varnishes, floor varnishes, etc., and also the stoving varnishes. 

The amount of oil used in “ short oil” varnishes varies from about 8 gallons 
to 16 gallons for every 100 lbs. of gum used. 

The amount of volatile thinners employed in varnishes is about 60 per cent., 
but this of course varies enormously according to the nature of the varnish and 
the method by which it is applied. For example, spraying and dipping varnishes 
are naturally of very low viscosity and contain a very high percentage of volatile 


thinners. 
VARNISH FORMULA 


No general formula and methods of working can be given for the preparation 
of the many varnishes which are usually sold in the trade for the reasons already 
given, but the recipes givén below, taken from Andés, Livache, and other well- 
known writers on this subject for the preparation of various varnishes which are 
in common use, will give some indication of the resins and the amount of oils and 
driers that may be used to produce such products :— 


(1) Finishing Body Varnish. (2) Hard Carriage Varnish. 


Gum Kauri : . 100 lbs. Pontianac resin : . 100 Ibs. 
Prepared oil 20 gals. Baltic linseed oil ; . 25 gals. 
Manganese resinate . : 4 lbs. Litharge . : : : 2 Ibs. 
Turpentine : : . 45 gals. Red lead . : : yA eae 
Manganese dioxide : 4G 
Turpentine : : . 50 gals. 
(3) Hard Church Oak Varnish. (4) French Oil Varnish. 
Congo copal gum ; . 100 lbs. Pale Sierra Leone copal . 100 lbs. 
Boiled linseed oil . . 22 gals. Bleached linseed oil : 25 gals. 
Sugar oflead_ . . ‘ 5 lbs. Cobalt acetate or linoleate 24 Ibs. 
Manganese hydrate . Aes Turpentine. : : 50 gals. 
Turpentine ; : . 42 gals. 


OIL VARNISHES 223 


(5) Furniture Varnish. (6) Flationg Varnish. 
Manila gum ; : . 100 lbs. Zanzibar copal . ‘ . 100 lbs. 
Boiled oil . : : - 18 gals. Baltic oil . : ." 15 gals. 
Stand oil : Sey Litharge . ; : ; 5 lbs. 
Prepared wood oil aes Manganese hydrate . ; Doty 
Turpentine or white spirit . 42 ,, Turpentine : . 935 -gals. 
(7) Japan Gold Size. (8) Shellac Gold Size. 
Kauri gum : : . 100 Ibs. T.N. shellac’. : . 100 lbs. 
Boiled oil . : . 22 gals. Prepared oil : . 80 gals. 
Red lead . : : 5 Ibs. Red lead . . 40 lbs. 
Litharge . ‘ F : ees Turpentine . 100 gals. 
Manganese dioxide. So 2 ae 
Turpentine ‘ ; . 45 gals. 


Japan gold size is used by sign-writers for lettering purposes with gold leaf, 
also, when thinned down, as a drier for paints, enamels and varnishes. 

Gold size should dry off hard in about two hours, and on account of this always 
contains a large amount of driers. 

It is also used as a medium in the preparation of quick-drying coach colours. 


(9) Cheap Dark Oak Varnish for inside (10) Pale Stoving Varnish. 
and outside use. 

Manila gum : : eno0 Ibs: Pale kauri gum . : . 100 lbs. 
Congo copal é ‘ peer DUE, Raw linseed oil . ‘ -~ _-18cgals, 
Raw linseed oil . : . ~ 20 gals. Turpentine ; ge POOR 55 
Litharge . ‘ 5 lbs. To stove at 220° F. No drier 
Manganese dioxide. : 253 is necessary. 
White spirit , . 45 gals. 


ROSIN VARNISHES': 


Colophony or rosin is largely used in the manufacture of the cheaper grades 
of varnish, more especially of those varnishes which are intended for indoor use. 

As varnishes made from mixtures of rosin and oil do not readily dry off hard, 
but tend to remain sticky or “ tacky,” it is customary to harden the rosin by the 
addition of lime or zinc oxide. 

Rosin may be hardened by dissolving it in white spirit or naphtha, and stirring 
in zine oxide or freshly slaked lime till it is all taken up. The usual method is 
to melt the rosin and add the required amount of lime to it at a temperature of 
about 300-400° F., stirring well till it is all cooked in, and a portion of the fused 
mass taken out is perfectly bright and clear when dropped on to glass. The clear 
fused mass is then thinned down to the right consistency with the necessary amount 
of turpentine or other suitable solvent. 

The lime combines with the rosin forming a calcium resinate whereby the 
acids of the rosin are neutralised. 

The ideal rosin varnish should be neutral, but in practice it is found that if 


224 THE CHEMISTRY OF PAINTS 


the neutralisation point is carried too far, the rosin-lime compound is insoluble in 
white spirit, turpentine, naphtha, etc. 

The amount of lime required to completely neutralise rosin (which has an 
acid value of 180) is roughly 9 per cent.; but as a rule not more than 5 per cent. 
of lime is used, whereby the acid value of the rosin is reduced to about 18. 

Rosin varnishes made by dissolving calcium rosinate or “ hardened” rosin 
in turpentine or white spirit dry very quickly, and with a high lustre; and as they 
are very cheap they are largely used as varnishes for indoor work and for making 
cheap varnish paints. 

As these varnishes are very brittle it is usual to add a proportion of boiled 
linseed oil to toughen them, but only a limited amount of oil can be used, other- 
wise such varnishes will not dry off hard enough to be satisfactory for general use. 


WOOD OIL VARNISHES 


In recent years large quantities of varnish suitable for both inside and outside 
use have been made by the addition of wood oil or tung oil to rosin or rosin esters. 

Rosin ester gum is the neutral product obtained 
by the complete esterification of the abietic acid of 
common rosin or colophony. It is not a pure 
chemical compound, as in addition to abietic acid 
rosin contains varying amounts of neutral unsaponifiable 
hydrocarbons, the proportions depending on the origin 
and method of manufacture of the rosin. 

Rosin ester gums are glycerides, and are manu- 
factured by combining rosin with glycerine (see 
page 163), whereby the acid value of the rosin is 
reduced to about 10. 

Ester gum varnishes are prepared in the following 
Fig. 43.—Sranparp_130-eatton way :—Hankow wood oil is heated up as rapidly as 

taken palaha se peas ots possible to 220° C. (428° F.) mm a copper, aluminium, 
SpectaL Bronze Borrom. or iron pot (see Fig. 43); 2 per cent. of litharge is 
then stirred in until completely dissolved, the 
temperature being allowed to rise to 260° C. (500° F.). The pot is then removed 
from the fire and allowed to cool down. The oil rapidly thickens up, and if allowed 
to go on cooling would solidify or form a jelly-like mass (polymerise). At this stage 
25 per cent. or more rosin ester gum is added and stirred well in. The ester gum 
melts and completely amalgamates with the wood oil, and if a sample be taken 
out and dropped on to glass it gives a tough, bright, transparent hard mass. 

When the contents of the pot have cooled to about 160° C. (320° F.) about 
4 or t per cent. of cobalt acetate or linoleate should be stirred in, after which turpen- 
tine or white spirit is added. 

Part of the wood oil may be replaced by stand oil if it is found that this 
varnish dries too rapidly or skins on the top after standing. 

















































































































OIL VARNISHES 225 


These varnishes on account of their low acidity possess the advantage of not 
thickening up or “livering” when mixed with either white lead, zinc oxide, or 
other pigments, and hence may be used as mixing varnishes. 

Wood oil ester gum varnishes are exceedingly durable and are eminently suitable 
for both indoor and outdoor use. Moreover, by reason of their excellent waterproof 
qualities, due to their wood oil content, they have been largely used as boat or 
yacht varnishes (spar varnishes). 

Wood oil varnishes are largely used on account of their great elasticity as the 
most suitable oil varnish for protecting doped fabric. 


SPECIFICATION FOR VARNISHES 


As there are so many different qualities of varnish manufactured, no general 
specification is of much use unless the particular purpose for which the varnishes 
are going to be used is known. 

The chief qualities required in a high-class varnish may nevertheless be 
enumerated briefly as follows :— 

The varnish should be bright and transparent, and free from any suspended 
matter, and when kept in a suitable container in a warm room for three months 
should not throw out any sediment or “foot.” This shows that the constituent 
parts are well amalgamated, and that the varnish has been tanked a sufficient 
time for it to age or mature properly. 

The paler varnishes are to be preferred to the dark ones provided that they 
dry off hard and without any tack within the required time. 

The varnish on drying off should give films of high brilliancy and lustre and 
not show any signs of blooming on exposure. 

The surface of the varnish should be perfectly smooth, free from picks or bits, 
and show no indication of ridging, crinkling or pin-holing. 

Outside varnishes should be tough and elastic, and on exposure to the weather 
should not crack or lose their lustre (“face ”’) after twelve months. 

Flatting or “ rubbing ” varnishes after drying off hard should rub down with 
pumice to produce a dull surface and not show any signs of sweating. 

Sweating in a flatting varnish indicates that too much oil has been used in 
its preparation. A flatting varnish is used as an undercoating varnish, and a 
finishing varnish will only adhere or “key on” if the under surface is perfectly, 
flat or “ matt.” A varnish if applied to a glossy surface does not adhere firmly, and 
on drying tends to “crawl” and become crinkly or, as it is commonly called “‘sisses.” 

The viscosity of the varnish should be determined in a suitable viscometer 
(Ostwald, Fig. 44 ) in order to see that it is equal to the standard required and that 
the right amount of volatile thinners has been used. 


LirHoGRAPHIC VARNISH, STAND OIL 


Lithographic varnish (litho or stand oil) is used in lithographic printing, in the 
manufacture of printers’ inks, and also in the manufacture of paints and enamels. 


226 THE CHEMISTRY OF PAINTS 


Stand oil is derived from the German word Standéle, because on standing the 
mucilage coagulates and separates out from these oils. 

Lithographic varnish is made by heating old clarified tanked oil in a large iron 
pan set in brickwork and provided with a hood to carry off the pungent acrid fumes 
which are formed. The furnace below the pot is bricked off, to secure that if, by 
any chance, the oil should boil over it cannot come into contact with the flames ; 
this affords a good protection against fire. The oil is gradually heated up to 250° F. 
and held at this temperature till all frothing has ceased, 7.e. till all the moisture 
has been driven off. The oil is then slowly raised to 570° F., and thence to 
610-620° F. This heat must be kept up until the oil has been brought to the right 
consistency. Any tendency to rise or boil over must be counteracted by adding 
a little cold oil. The time required to thicken up the oil varies from about two 
hours heating to ten hours, according to the strength or thickness of the finished 
product. 

Lithographic varnish is also made by heating up linseed oil to its ignition point 
in large movable iron pans. The pans are then withdrawn from the fire and the 
issuing vapours ignited by means of a lighted taper. The oil burns with a pale 
blue flame, which gradually becomes luminous and smoky. At this stage the fire 
is put out by placing a large piece of sheet iron over the pot and thus excluding all 
the air. 

The pot is again put on to the fire and heated up, and the igniting process 
repeated, and so on till samples taken out and cooled down indicate that the oil 
has reached the desired consistency. Litho varnishes are manufactured in the 
following consistencies :—Tint, thin, middle, strong, and extra strong. 

Stand oils are usually sold for use in paints and enamels, and are of a medium 
consistence. They sometimes contain a small proportion of driers, when they are 
known as drying stand oils. 

They should be pale in colour, and must not be sticky, and should dry with a 
good gloss. 

When linseed oil is heated it gradually thickens, and its gravity increases, 
while the iodine value falls. This thickening of linseed oil on heating is due to 
polymerisation. 

The following figures obtained by the author on heating linseed oil on the large 
scale for the manufacture of stand oil will indicate the changes taking place during 
this process :— 


Time of Gravity Free Saponific- 


: : : Todine 
lou °C old, Value Value. 
0 Linseed oil . 4 . 09320 2°5 191-5 184-0 
2 Extra thin stand oil . 0°9452 3°19 186°5 157-0 
3 Thin stand oil : . 0-9465 3°85 178-4. 123-2 
4 Medium stand oil . . 0-9574 4-43 183-8 115-4 
5 Stout stand oil . . 0°9650 5-34 185-0 111-5 


OIL VARNISHES 227 


ANALYSIS OF Ori VARNISHES 


The complete analysis of oil varnishes, by which we mean the identification 
and estimation of the amount of the particular gum resins, and also the oils which 
have been used in their preparation, is, in the present state of our knowledge, quite 
impossible, in spite of many statements to the contrary. 

This can easily be realised when one considers that varnishes are very often 
made up from mixtures of two or more gum resins in conjunction with linseed oil, 
or mixtures of linseed oil, wood oil and stand oil, and that during the process of 
fusion and amalgamation they undergo very considerable changes, being both 
oxidised and polmerised, so that even if processes could be 
devised whereby the ingredients could be separated from one 
another the products thus obtained would show little if any of 
the characteristics of those originally used. 

Fortunately, however, the complete analysis of a varnish in 
this sense is not required, and all that is necessary is to be able 
to evolve a scheme whereby such products may be classified and | 
duplicated. 

The usual procedure in the examination of a varnish of # | 
unknown composition is to subject it to a series of physical and | 
chemical tests and to compare the results with similar tests on 
varnishes of known composition ; by this means much valuable 
information may be obtained by anyone familiar with the different 
gums used, and the various and intricate details of varnish 
manufacture. % Ete ‘ 2 ; Fic. 44.—OstwaLp 

In this way no difficulty will be found in matching a varnish —-Viscomerzr. 
with one which, although it may not contain identically the 
same constituents (gums, oils, etc.), will nevertheless be its equal for all practical 
purposes. 





(1) General Appearance 


The sample of varnish under test is placed in a standard varnish tube and its 
colour and “run up” or viscosity compared with that of other standard varnishes 
placed in identically similar tubes. The viscosity may, if required, also be 
determined accurately in an Ostwald viscometer (Fig. 44). 

Simple form of Ostwald Viscometer—This apparatus consists essentially of two 
glass tubes of different diameters joined together at one end, while the narrower 
tube has a bulb blown near the free end. A mark “ A” is made on the glass a little 
above the bulb, and a second, “ B,” is made some distance below the bulb. Excepting 
where very viscous liquids are under examination, it is desirable that the tube from 
the lower end of the bulb to just below the mark “ B” should consist of capillary 
tubing. 

To use the apparatus it should be kept in a thermostat, and a convenient amount 
of the varnish should be introduced through the wider tube by means of a mouthpiece 
attached to the top of the narrower tube; varnish is drawn up into this arm until 


228 THE CHEMISTRY OF PAINTS 


its level is above the mark A. The varnish is then allowed to fall in the tube 
under the action of gravity, the time taken for the surface to fall from A to B being 
carefully observed with a stop watch. This interval is then compared with that 
obtained for a standard varnish of known viscosity under the same conditions in the 
same viscometer. . 

The smell of the varnish will give a good general idea as to its value. A 
pleasant gummy, aromatic, turpentine odour indicates a high-class varnish, which 
has been made up from gum resins and thinned down with turpentine; whereas 
varnishes which contain large amounts of rosin, or rosin and wood oil, and petroleum 
thinners possess a peculiar smell, readily identifiable by anyone who is at all familiar 
with these products. 

If the varnish be at all turbid or cloudy it is an indication either that the driers 
have not been properly incorporated during the process of manufacture, or that 
the varnish has not been tanked long enough. Very often a varnish may cloud 
or “throw out” if brought from a warm room and left for some time in the cold. 
Turbid or cloudy oil varnishes always give unsatisfactory results, and only bright 
and clear varnishes should be used. 

The viscosity of a varnish varies considerably according to the nature of the 
varnish and its method of application. 

Finishing varnishes, such as body and carriage varnishes, which are to be 
applied by a brush, should be of stout consistency or body so that good flowing 
coats may be applied, which will dry off with a high lustre. Undercoating varnishes, 
flatting varnishes, etc., are as a general rule of a much thinner consistency, as they 
are required to dry off quickly with hard surfaces and are not required to have any 
particularly high gloss. Gold size and rosin varnishes are usually low in viscosity. 


(2) Working Properties 
The working and flowing properties of a varnish will give valuable indications 
of its quality. A high-class varnish will brush out easily without any pull and flow 
evenly over the surface to which it is applied. Cheap varnishes containing rosin 
are difficult to work and “lay off” and soon begin to pull on the brush. Some 
varnishes show an objectionable tendency to froth or bubble when worked under 
the brush, due to the high volatility of the solvent used in thinning them down. 


(3) Tome of Drying 

The time of drying of a varnish should always be carefully noted, as this gives 
an excellent indication of the nature of the varnish under examination. The time 
of drying varies considerably, e.g. a high-class elastic finishing body varnish will 
require, at ordinary room temperature, about twelve to fourteen hours to dry off 
hard, while a gold size, on the other hand, should dry off in about one to two 
hours. This test is usually carried out by flowing the varnish on to a glass strip 
and placing it in a vertical position; the times which the varnish takes to become 
“tacky,” “surface dry,” “dry” and “hard dry” are then noted. 


OIL VARNISHES 229 


Varnishes containing untreated wood oil, or wood oil that has not been properly 
polymerised, show a tendency to “web” or “crocodile skin” when the film on 
glass is allowed to dry in a cupboard exposed to the fumes from a coal gas flame. 

A sample of the varnish should also be brushed on to a prepared board, and 
the time of drying noted in this case also, so as to check the results obtained on the 
glass strips. 


(4) Nature and Characteristics of the Dry Film 


An examination of the dried varnish films when perfectly hard is of great value 
in ‘estimating their toughness and elasticity. The tougher and more elastic the 
films are, the greater the durability and weather resisting properties of the varnish. 

A varnish which yields hard yet brittle films, such as is the case with rosin 
varnishes, wear badly on exposure to the weather; this is due to the action of the 
rain and moisture and variations in temperature causing contraction and expansion, 
whereby the films crack and perish in a very short time. 

The toughness of a varnish may be judged by taking the dried film on glass and 
scratching it with the thumb nail or with a sharp instrument such as a knife blade. 

The brittle varnishes will powder up and dust off readily, while the tough 
varnishes may be scraped off in the form of tiny ribbons. 

In these tests care must be taken to see that the varnish film is perfectly hard 
and dry throughout, otherwise the test will not be accurate. 

A good plan is to test the film of varnish at intervals of time extending over a 
couple of months or more, so as to get absolutely reliable information, since not 
infrequently varnishes which are moderately tough after two or three days drying 
become very brittle after keeping for some time. 

Another method consists in varnishing a piece of thin tin plate and, after the 
varnish is thoroughly dry, bending the tin and noting the condition of the varnish 
after it has been subjected to this strain. 

The hardness of a varnish may be tested and a numerical value given to it by 
an instrument devised by A. P. Laurie and F. G. Baily. 

An apparatus described by H. Wolff consists of a triangle formed by three 
wooden strips, the base of which is hinged to the face of a base board. At the apex 
of the triangle is fitted a blunt knife edge directed towards the face of the base 
board. Pressure is exerted on the knife edge by means of a small loaded dish set on 
the apex directly over the knife edge, and so arranged as to be counterpoised to 
zero load by a lever carrying a sliding weight, and set at right angles into the hinged 
base of the triangle in a direction away from the apex. 

The varnish test plate is fixed to the two strips which slide in guide rails fastened 
to the base board, and is moved at a definite rate so that the film comes in contact 
with the knife edge. 

By means of a paper scale attached to the test piece a number of “ cuts” can 
be made at varying loads and compared. 

By substituting a strip of tinned iron in place of the knife edge and taking 


1 Farben Zeitung, August 1922 (0.C.T.J., 1922). 


230 THE CHEMISTRY OF PAINTS 


observations at loads slightly above zero the progress of drying of a varnished surface 
may be noted by the adhesion or otherwise of the testing edge. 

The dry film of varnish on wood should also be tested by rubbing down with 
sandpaper and noticing how it works under such treatment. 

Only flatting varnishes which are “short oil” varnishes will rub down in a 
satisfactory manner, giving perfectly flat surfaces, which do not sweat, and to which 
a subsequent coat of finishing varnish will adhere firmly. 


(5) Weathering and Waterproof Properties 


The weathering tests on a varnish should be carried out in the following 
manner :—Prepared boards varnished with one and two coats of the varnish under 
test are hung up outside in an exposed position and examined from time to time. 

Cheap rosin varnishes will spot in a few days, and after a few weeks will crack 
all over. On the other hand, outside varnishes, such as elastic oak varnish, etc., 
will keep their gloss or “ face ” and show little signs of wear even after twelve months’ 
exposure. 

Varnishes which contain an excess of driers are found to wear badly on 
exposure, as such excess plays a very active part in favouring speedy “ super- 
oxidation,’ whereby the film is rapidly corroded and perishes. 

As such exposure tests take time, and very often it is desirable to form some 
estimation of the wearing properties of a varnish in a few days, the author has 
found that fairly good results may be obtained as to the durability or wearing 
properties of a varnish by immersing the dried films in a dilute solution of sulphurous 
acid, then allowing to dry out in the open air. 

The waterproof qualities of a varnish are best determined by immersing 
varnished strips of tin in a bow! of water for twelve hours, then removing and allowing 
to dry in the open. The varnishes which contain much rosin remain more or less 
permanently white, and this also applies to some of the softer gum varnishes. 

Dammar varnishes, and varnishes made up of wood oil and a small proportion 
of ester gums, are remarkably waterproof and on exposure to water are little 
affected; if subsequently dried they again become bright and clear, without 
showing any signs of corrosion. 

A simple test, which is very often carried out by coach-painters, consists in 
placing a wet sponge on their varnished work after it is thoroughly dry, and leaving 
over night. Next morning the varnish should show no change of colour, and if 
gently rubbed with a soft cloth should polish up bright and dry and leave no trace 
of the application of the sponge. 


ANALYTICAL EXAMINATION 


The methods in general use for the analytical examination of varnishes are 
briefly as follows :— 

The specific gravity, viscosity and acid values are first determined in the usual 
manner. 


se 


OIL VARNISHES 231 


Driers 


The next procedure consists in ashing 5 or 10 gms. of the varnish, weighing 
the ash, and estimating the percentage of metallic driers present by following the 
method given on page 248; or, alternatively, the driers may be extracted by 
agitation with hydrochloric acid. 


Volatile Matter 


The volatile matter is determined by weighing out 100 gms. of the varnish 
into a flask connected with a condenser. The varnish is heated in an oil bath 
gradually to about 130° C., and a current of steam is pressed through till all the 
volatile matter is driven off. A rough determination may be quickly made by 
heating 10 gms. of the varnish on a sand bath till no more volatile matter is 
driven off, but owing to the high temperature necessary to drive off all the volatile 
constituents of the varnish, decomposition is liable to take place, and this would 
cause the result obtained to be too low. 

The residue obtained gives the amount of oil and resin present in the varnish. 


Separation of Oil and Resin 


The separation of the oil and resin constituents of a varnish is carried out 
by first saponifying the residue obtained (after the removal of the volatile con- 
stituent), by boiling with alcoholic potash under a reflux condenser until as complete 
saponification as possible has taken place. The unsaponifiable matter is extracted 
with ether in the usual way, and the resin oil soap solutions are acidified with 
hydrochloric acid and taken up with ether. The ether is removed by distillation, 
the fatty acids and gums dissolved in absolute alcohol and esterified by passing in 
dry hydrochloric acid until saturated (Twitchell’s method). 

In this way the fatty acid esters are separated from the resin acids and the 
total amount of resins present in the varnish estimated. 


CHAPTER XIX 


THE MANUFACTURE OF SPIRIT VARNISHES, 
CELLULOID VARNISHES, LACQUERS AND DOPES 


Sprrir varnishes are made by dissolving resins in oil of turpentine, alcohol, acetone, 
and other volatile solvents without the addition of any drying oils. These varnishes, 
as a tule, dry off very quickly, with a high lustre, and hence are largely used as 
protective coatings for indoor work where quick results are required. 

The manufacture of spirit varnishes is an extremely simple operation, and 
is carried out usually 
by dissolving the resins 
in the cold in the various 
selected solvents in the 
following manner :— 

The broken-up resin 
is emptied into a large 
barrel, which is fixed on 
to supports on which 
it can revolve (Fig. 45). 
The required amount of 
solvents is added, the 
cover screwed on, and 
the contents churned for 

Fie. 45.—Spirir VarnisH CHURN. a few hours till solution 
has taken place. 

In the case of the higher boiling paint solvents it is usual to melt up the resins 
in a steam pan or by direct heat over a fire, and then to stir in the solvent; or, 
alternatively, to warm up the solvent and stir in the finely-powdered resins. 

By this means the process of dissolving the resins is very considerably 
accelerated. The varnishes may be filter pressed to remove any suspended matter. 











ALCOHOLIC SpirIT VARNISHES 


The most important of the alcoholic spirit varnishes, and the one in most 
general use, is shellac varnish, which is manufactured in large quantities for use in 
the polishing of furniture, and is sold under the name of French Polish. 

French polish is made by dissolving shellac in methylated spirit in the cold 

232 


SPIRIT VARNISHES AND LACQUERS 233 


in the following manner :—5 lbs. of Venice turpentine and 60 Ibs. of orange shellac 
are churned for six hours with 40 gallons of methylated spirits. The resulting 
varnish has an orange-brown turbid appearance, and dries in about ten minutes, 
with a hard lustrous coat. The Venice turpentine helps to toughen the film and 
so increase its durability. 

This varnish is applied with a rubber; a large number of exceedingly thin 
coats are laid on to the article which is being polished, and by this means a beautiful 
lustrous finish is obtained. 

For white varnishes bleached shellac is used; for dark varnishes ruby or 
garnet shellac. © 

Knotting varnishes, which are so largely used by painters as a first coat or 
priming on wood, are also prepared by dissolving shellac in methylated spirits. 

In place of ethyl alcohol some manufacturers use methyl] alcohol, more especially 
in America; but on account of its toxic qualities its use is not to be recommended. 


Wuite Harp Spirit VARNISHES 


These varnishes are made by dissolving spirit soluble Manila gums in alcohol 
or methylated spirits, usually about 3 lbs. of Manila gum to 1 gallon of alcohol 
being the proportion adopted. They are clear, transparent varnishes and are 
largely used as paper varnishes. 

For making spirit Manila varnishes only those copal gums should be selected 
which will readily dissolve to a clear solution, free from slimy or stringy qualities. 
They dry off very quickly with a high lustre. 


Brown Harp Spirit VARNISH 


This varnish is made in a similar manner to white hard spirit varnish, but a 
small percentage of Bismarck brown is added to give the requisite colour. 


Rostn ALCOHOLIC SPIRIT VARNISHES 


These are made by dissolving pale rosin in alcohol, about 4 lbs. of rosin to 
1 gallon of alcohol. They are rather brittle, hence are only used for common work. 

In addition to the resins already mentioned, many others can also be used in 
alcoholic solution for the preparation of quick-drying lustrous varnishes, among 
which may be mentioned gum mastic, sandarac, elemi, etc. 

Various softening agents may be used in small proportions in conjunction 
with the above-mentioned resins in order to toughen their films and prevent them 
from flaking off. The usual ones employed are castor oil, Venice turpentine, gum 
thus, copaiba balsam, and Burgundy pitch. 

The following recipes taken from Livache, Bottler, Hurst, and others will 
give a general indication of the various proportions which are commonly employed 
in the preparation of alcoholic spirit varnishes, and the purposes for which they 
are used :— 


: 


234. THE CHEMISTRY OF PAINTS 


(1) Dark Brown Polish. 


(2) Whate Polish. 


Garnet shellac 40 lbs. Bleached shellac 40 lbs. 
Methylated spirit 25 gals. Methylated spirit 27 gals. 
(3) Shellac Spirit Varnish. (4) Bookbinders’ Varnish. 
Orange shellac 10 lbs. Shellac 82+ Ibs. 
Venice turpentine ; 3 5 Spirits of turpentine . 3 gals. 

Alcohol 36 gals. Methylated spirit . 20S 
(5) Paper Varnish. (6) Rosin Varnish. é 
Sandarac . ‘ = =< bOolbs. Pale rosin 23 Ibs. 
Thick turpentine heey ou a Venice turpentine. ; 4 ,, 
Alcohol 15 gals. Alcohol. : Rese? | tice 
(7) Paper Varnish. (8) Bookbinders’ White Varnish. 
Manila copal 16 parts Sandarac . : 6 parts 
Venice turpentine : , eee Mastic . : : i haere 
Alcohol, 95 per cent. . eR DOE ne, Elemi : : : 7: ae 
Alcohol . : : BO 


(9) Negatwe Varnish for Photographers. 


Gum sandarac 5 ozs. 
Gum benzoin Dy aes 
Methylated spirit + gal. 


CoLOURED LACQUERS 


Coloured lacquers are made in large quantities for colouring metals, wood, 
leather goods, etc. They are applied to metals in two ways, known as “ cold 
lacquering ” and “ hot lacquering.”’ 

The colouring of the lacquers or spirit varnishes is usually effected by adding 
to them concentrated alcoholic solutions of aniline dye-stuffs. Formerly the 
naturally occurring colouring substances such as dragon’s blood, turmeric, gamboge, 
logwood extract, and others were used for this purpose, but at the present time 
these have been replaced by spirit aniline colours. These colours are soluble in 
alcohol, and are manufactured in all tones and shades suitable for different types 
of work. The following recipes for the preparation of various coloured lacquers 
will give a general idea as to their composition :— 


(1) Deep Gold Lacquer. 


(2) Pale Gold Lacquer. 


Bleached shellac 3 Ibs. Bleached shellac 10 ozs. 

Methylated spirit 2 gals. Methylated spirit 1 gal. 

Concentrated solution of Dia- Aniline yellow concentrated 
mond-Fuchsine + pint solution + pint 


SPIRIT VARNISHES AND LACQUERS 235 


(3) Blue Lacquer. (4) Violet Lacquer. 
Shellac. : ; aD ZE, Shellac : : oe ae. 028, 
Sandarac . ; : ue es en Sandarac . : ; EEGs 4.3; 
Elemi : Bit 2 Elemi oer! 
Alkali blue Eecantratell lke Methylated cit 1 gal. 

tion . : : 4 pint Methyl violet fponccumatad 
Methylated eer : eat A agal: alcoholic solution) : + pint 


Spirit Varnish Stains are largely used for the staining of wooden floors, etc. 
They are made by adding Vandyke brown, Bismarck brown, and other colouring 
matters to shellac, Manila and rosin spirit varnishes. 


TURPENTINE SPIRIT VARNISHES 


These spirit varnishes may be made by dissolving the resins in the turpentine 
(or turpentine substitutes such as white spirit, benzol, etc.) in the cold in precisely 
the same way as described under the alcoholic spirit varnishes. 

In general, however, it is customary to melt up the resins and stir in the volatile 
solutions, as by this means much quicker solutions are obtained. Turpentine 
varnishes dry more slowly than alcohol varnishes, hence are more easy to apply. 


DamMarR VARNISH 


This varnish is largely used as a paper varnish under the name of crystal paper 
varnish. It is also used in the preparation of white enamels, as, on account of its 
low acidity, it can be mixed with zinc oxide without any “ livering” or thickening 
up taking place. The enamels thus prepared are of a pure white colour and dry 
quickly with a high gloss. 

Dammar varnish is prepared by melting pale dammar gum and thinning down 
to the right consistency with turpentine or white spirit. The following proportions 
may be used :— 


Dammar . ; : . 10/ozs. 
Sandarac . : " PE wre 
Mastic A ; : Bo Lede 
Turpentine ; : PaaS. 


The mastic and sandarac gums are added to give toughness and elasticity to the 
varnish. 


Rosin, TuRPitone SPrrir VARNISHES 
These varnishes may be prepared by churning rosin or hardened rosin with 
turpentine till solution is effected, or the rosin may be melted and the turpentine 
stirred in till the required consistency is obtained. 
White spirit and naphtha are often used in place of turpentine to cheapen the 


varnish. 
Rosin spirit varnishes are largely used as furniture varnishes and cheap oak 


236 THE CHEMISTRY OF PAINTS 


varnishes for inside work. They dry with brilliant glossy surfaces, but are too 
brittle to be very serviceable, and are liable to powder off on rubbing. 

They are also used in the manufacture of common quick-drying varnish 
paints with the addition of pigments such as red oxide, lithopone, carbon black, 
and so on. 


The Analysis of Spirit Varnishes 


The analysis of spirit varnishes is very much easier matter than that of an oil 
varnish. The volatile matter is estimated by evaporating about 5 gms. of the 
sample in a steam oven till constant in weight. The residue is then tested for rosin 
by the Liebermann-Storch reaction (see page 162). 

A small portion of the residue is next ignited, when, if shellac be present, 
it will be readily detected by the characteristic odour which it gives off on 
burning. 

The determination of the iodine value of the residue will give approximately 
the proportion of shellac present in a mixture of rosin-shellac varnish. In 
calculating the results the iodine value (Wijs) of shellac is taken as 18 and 
that of rosin as 228. 

In the case of dammar varnishes the amount of rosin present may be ascertained 
by determining the acid value, taking the acid value of dammar as 20 and that of 
rosin as 180. 

The nature of the volatile solvents may be accurately determined by distilling 
about 100 gms. of the varnish and examining the distillate in the usual manner. 


CELLULOID AND NITROCELLULOSE VARNISHES 


When cellulose (cotton wool, cotton waste, etc.) is treated with a mixture 
of nitric and sulphuric acids, it is converted into pyroxyline or gun cotton— 
CyoHy4(NO.),04, or into dinitrocellulose. 

Nitrocellulose is converted into celluloid by mixing it with camphor and heating 
under pressure. Both gun cotton and celluloid are largely used at the present time 
in the manufacture of varnishes and lacquers. 

These varnishes are made by churning nitrocellulose or celluloid with amyl 
acetate or butyl acetate to a syrupy consistency, then thinning down to the 
required consistency with a mixture of equal parts of alcohol and benzol. In place 
of alcohol and benzol other solvents may be used such as ether, acetone, etc. 

Nitrocellulose and celluloid varnishes are perfectly clear, colourless varnishes, 
and are very volatile and highly inflammable. They are extensively used as 
transparent lacquers for metal work, etc. ; for decorative work they may be coloured 
with various aniline dye-stuffs soluble in the lacquer. ; 

Various pigments such as zinc oxide, carbon black, iron oxide, etc., ground in 
castor oil and thinned down with these varnishes are now in general use as protective 
coatings for metal work, doped aeroplane fabric, and so on. They are usually 
applied by spraying, and dry off rapidly, giving beautiful, tough, hard films. In 
recent years they have come rapidly into favour on account of their many valuable 


SPIRIT VARNISHES AND LACQUERS 237 


properties, and have for many purposes replaced stoving and air-drying varnishes 
and enamels. 

Softening agents such as castor oil, dammar gum, Canada balsam, and other 
soft resins are usually added to these lacquers and enamels to toughen them, and 
at the same time to enable them to “ key on” more readily to the surfaces to which 
they are applied. 

Nitrocellulose varnishes are also sold under the name of collodion and zapon 
varnishes. 


Dope 


Cellulose acetate varnishes, commonly known as “ dope,” are used for rendering 
the fabric on aeroplane wings taut. They are brushed on to the fabric in situ, one 
coat being laid on the other. About four coats of varnish are usually necessary in 
order to obtain the desired tautening effect. 

Cellulose acetate, prepared by treating cellulose with acetic anhydride, is 
a soft white fibrous material which, unlike gun cotton, has the merit of being 
non-flammable. 

The varnish is prepared by stirring the cellulose acetate into a mixture of 
acetone (or calcitone, methyl ethyl ketone), benzol, and alcohol, sufficient solvent 
being used to give the desired viscosity. A small proportion of softening agents 
such as benzyl alcohol, triacetin, triphenylphosphate, etc., are added in order to 
toughen the films given by the varnish on evaporation. 

Formerly tetrachlorethane was used as a solvent for cellulose acetate in the 
manufacture of dope, but owing to its toxic properties its use was abandoned. 

Dope is a clear, transparent varnish which when poured on to glass quickly 
evaporates, giving perfectly clear, tough, transparent films, which may be readily 
removed from the glass. The presence of excess of moisture, or unsuitable softening 
agents, will cause the films to dry off white and be brittle, in which case the varnish 
should be condemned. 

Owing to its poor weather-resisting properties it is usual to protect the doped 
fabric with pigmented cellulose nitrate varnishes, those of a reddish or khaki colour 
affording greater protection than those coloured with white or light tints. 


Pigmented Dope 


This is prepared by adding a small percentage of pigments (usually of a reddish 
or khaki colour) finely ground in a medium of triacetin or benzyl alcohol to the 
cellulose acetate varnishes. It is used in place of ordinary clear dope on account of 
its greater durability and wearing qualities, and thus avoiding the necessity of 
applying a pigmented protective coating over them. 

Dopes made on a nitrocellulose basis, and to which certain materials have been 
added to render them non-inflammable, are also used in place of cellulose acetate 
dopes. They are considered to be fully equal if not superior to dopes made from 
cellulose acetate as regards durability and tautening properties. 


238 THE CHEMISTRY OF PAINTS 


CHINESE AND JAPANESE LACQUER 


Natural lacquers are obtained from various species of trees, both native and 
cultivated, which grow in China, Japan, India, Ceylon and Burma. 

Chinese and Japanese lacquer is the liquid sap of the Rhus vernicifera D.C., 
a species of the lac tree, which is grown extensively in Japan. The liquid sap known 
as “ kiurushi”’ exudes on making cuts on the trees in the form of a thick, creamy, 
light-coloured fluid, of a specific gravity of 1-002, which rapidly darkens on 
exposure. 

It contains from 64 to 85 per cent. of urushic acid (C,,H,,0,) and 9 to 26 
per cent. of water, 3 to 6 per cent. of gum arabic, together with a little oil and 
albuminous matter. 

These natural lacquers possess the remarkable property of drying more rapidly 
in a damp atmosphere than in a dry one, owing to a fermentation process which takes 
place whereby the urushic acid becomes oxidised to oxy-urushic acid ©,,H,,0s. 
This varnish has been used by the Chinese and Japanese from a very remote period 
(according to Quinn from 500 to 600 B.c.) for the lacquering of their wares. 

The results obtained by the Japanese with these natural lacquers is truly 
remarkable, excelling all other varnish work as regards the beauty and lustre of 
the finish obtained. 


CHAPTER XX 
DRIERS OR SICCATIVES 


As the drying oils which are used in the manufacture of paints and varnishes 
set, at ordinary temperatures, far too slowly for the purpose for which they 
are usually intended, it is necessary to add to them certain metals or their 
compounds in order to accelerate this drying or setting process. Such additions 
are known as driers or siccatives, and by their aid paints and varnishes which 
in the ordinary way would take two or more days to dry can be made to dry in 
a few hours. 

According to Fokin the following metals or their compounds assist the 
oxidation or drying property of linseed oil in the following order, arranged according 
to their activity :—Cobalt, manganese, chromium, nickel (iron, platinium palladium), 
lead, calcium, barium, bismuth, mercury, uranium, copper, zinc. 

He also shows that the rapidity of the reaction varies in proportion to the cube 
root of the concentration of the drier. 

According to Hartley, Mulder and others, the function of the drier is to act as 
a catalyser or an oxygen carrier, taking up oxygen from the air and transferring it 
to the oil, and in so doing undergo alternately the opposite processes of oxidation 
and reduction. In support of this theory it is noteworthy that the metals which 
are the most effective as catalysers are those which readily form higher and 
lower oxides. 

The above-mentioned metals (in an extremely fine state or sub-division) may be 
used as driers, but in practice it is found more convenient and efficacious to use 
oxides and salts—especially certain organic salts—of these metals. 

The principal substances used commercially as driers are the oxides or salts 
of lead, manganese, and cobalt as follows :— 


LEAD DRIERS 


Litharge (PbO). 
Red Lead (Pb,0,). 
Lead Acetate or Sugar of Lead (Pb(C,H,0,).+3H,9). 
Lead Resinate. 
, Lead Linoleate. 
Lead Tungate. 


240 THE CHEMISTRY OF PAINTS 


MANGANESE DRIERS 


Manganese Dioxide, Black Oxide of Manganese (MnQ,). 
Manganese Hydroxide, Umber (Mn(OH),). 

Manganese Borate (MnB,0,). 

Manganese Acetate (Mn(C,H,0,),). 

Manganese Chloride (MnCl,), 4H,0. 

Manganese Sulphate (MnSO,), 5H,0. 

Manganese Resinate. 

Manganese Linoleate. 

Manganese Tungate. 


CoBALT DRIERS 


Cobalt Acetate. 
Cobalt Linoleate. 
Cobalt Resinate. 


Recently oxides and salts of vanadium have been used as driers, and it is 
claimed that these bodies act most vigorously as catalysers even when present in 
very minute proportions. It is doubtful, however, if they will come into general 
use, as, comparatively, their cost is high and they tend to darken the oils in which 
they are dissolved. 

Zinc oxide and zinc sulphate are also occasionally used as driers—usually in 
conjunction with lead or manganese; but as their drying properties are extremely 
small their value as driers is problematical. 


LEAD DRIERS 
LitHarce (PbO) 


Litharge or lead monoxide is obtained when metallic lead is oxidised at high 
temperatures. It comes on to the market in the following forms :— 

Canary Litharge-—A pale yellowish coloured powder, with an extremely fine 
and soft texture. 

Ordinary Litharge.—A reddish yellow powder; and 

Flake Litharge, a coarse glistening flaky powder of a reddish colour. 

All three forms of litharge may be used as driers, and on heating with linseed 
oil readily dissolve, forming a drying oil, which will dry at ordinary room temperatures 
in about eight to twelve hours. 

The amount of lead required to make an oil or varnish dry in a reasonable 
time is comparatively small, 0-5 to 2 per cent. being about the usual proportion 
necessary, except in those cases, such as in the manufacture of gold size (see page 223), 
where the material is required to dry off in an hour or two, when much larger 
quantities are necessary. 

The chief impurities in litharge are metallic lead, lead sulphate and red lead, 
all three usually being classed together as insoluble matter. 


DRIERS OR SICCATIVES 241 


The purity of a litharge may be ascertained by boiling 5 gms. with dilute 
acetic acid, filtering in a Gooch crucible, washing well with hot water, drying 
and weighing. The insoluble matter should not exceed 0-5 per cent. 


Rep Leap 
See Chapter X., page 114. 


Leap Acetate (NEUTRAL) oR SuGAR oF LEAD 
(Pb(C,H;0,)2+3H,0. ) 


Lead acetate or white sugar of lead is manufactured by dissolving lead or 
litharge in acetic acid and crystallising out. To obtain it in its finest form it is 
necessary to recrystallise. 

It crystallises in transparent colourless rhomboidal prisms, which whiten on 
exposure to the air. It has a sweet unpleasant metallic taste, and smells slightly 
of acetic acid. 

It dissolves readily in ordinary water, giving as a rule a white turbid solution, 
which may be cleared by the addition of a few drops of acetic acid. The turbidity 
is due to the lime present in the ordinary tap water, which precipitates finely 
divided white lead hydrate, which again dissolves to a clear solution on the addition 
of acetic acid. 

Crystallised lead acetate melts at 75° C.; at higher temperatures it decomposes 
into lead carbonate and acetone. It is slightly soluble in alcohol. 


Basic Sucar or LEAD 


Sugar of lead has the property of dissolving considerable quantities of litharge 
forming basic salts. Thus when one equivalent of neutral acetate of lead solution 
is boiled with one or two equivalents of litharge we get formed respectively di-basic 
and tri-basic lead acetate. 

Sugar of lead comes on to the market in the following forms :— 


1. White sugar of lead, ¢.e. normal or neutral lead acetate. 


2. Grey sugar of lead, ; 
3. Brown sugar of lead, } Basic sugar of lead. 


Sugar of lead is an excellent drier, and is largely used for this purpose, both 
in paints and varnishes, and is an essential constituent in the patent paste driers, 
which are so largely used by painters for making their mixed paints dry off quickly. 


LEAD RESINATE 


Precipitated or Fused 


Lead resinate may be made by either of the following processes :— 

1. Precipitation Process.—Rosin is boiled up with a dilute solution of caustic 
soda until it is completely saponified. A solution of sugar of lead is then run into 
the rosin soap solution, and vigorously stirred until all the rosin is completely 


242 THE CHEMISTRY OF PAINTS 


precipitated. The precipitated lead resinate (or rosinate) is then well washed with 
hot water and dried at a low temperature. Precipitated lead resinate is a brownish 
coloured brittle solid, and as sold usually contains about 17 per cent. lead. 

2. Fusion Process.—Rosin is melted up in a large pan and finely divided 
litharge is gradually stirred in at about 300-450° F. Considerable action takes 
place and the lead dissolves completely in the rosin, forming a bright clear mass. 
Fused lead resinate comes on to the market in the form of dark-coloured brittle 
lumps, and contains as a rule about.10 per cent. of metallic lead. 

Lead resinate made by the precipitation process may be readily distinguished 
from the fused lead resinate, as the former always contains traces of moisture. 

Lead resinate is soluble in hot linseed oil, wood oil, turpentine or white spirit, 
and is largely used as a drier for boiling oil as well as a drying agent in the manu- 
facture of varnishes. Dissolved in turpentine, it forms the patent liquid driers 
which are so largely sold under the name of “ terebine.” 


Leap LInoLeateE (Precipitated) 


Lead linoleate is prepared by saponifying linseed oil with the requisite amount 
of weak caustic soda solution, then running in with vigorous stirring a solution 
of lead acetate. The brownish sticky mass of lead linoleate thus formed is well 
washed and dried at a low temperature. It is an excellent drier, and is largely 
used in preference to lead resinate on account of its toughness and elasticity, which 
far surpasses that of the rather brittle resinate of lead. As a rule it contains about 
25 per cent. of metallic lead. It readily dissolves in turpentine, linseed oil, etc. 


Leap TuncaTE (Precipitated) 

Prepared from wood oil, or from wood oil fatty acids in a similar manner to 
that described above under Lead Linoleate. 

Lead tungate is an exceedingly powerful drier, and far exceeds in this quality 
lead linoleate. Of late years it has come into considerable favour as a drier on 
account of its ready solubility in oils and its property of producing very little 
“ footing ”’ out in the medium in which it is used. 


Fusep Leap LINOLEATE AND TUNGATE 


Fused lead linoleates and tungates are produced by dissolving litharge in hot 
linseed oil or wood oil or their fatty acids. They usually contain about 25-30 
per cent. of metallic lead. 


MANGANESE DRIERS 
MancGAneEsE Diox1pE (Mn0,) 


(Black Oxide of Manganese.) 


Manganese dioxide occurs naturally as pyrolusite and is the raw material from 
which the various salts of manganese are prepared. 


ae 2 


DRIERS OR SICCATIVES 243 


It comes on to the market for use as a drier in the form of a very finely ground 
black powder containing about 90 per cent. MnO,. It is extensively used as a 
varnish drier, as it requires a fairly high temperature before it will go into solution. 
Although an exceedingly good drying agent it has unfortunately the drawback 
that it tends to darken the oils with which it is heated. 

On account of only being soluble at comparatively high temperatures it is not 
used as a paint drier. 


ManGANESE SuLPHATE (MnSO,), 5H,0 


This salt is prepared by dissolving manganous oxide or carbonate in sulphuric 
acid. It is a white salt with a faint pink colour. It is used as a drier in pre- 
ference to manganese dioxide, as it is more soluble, and, moreover, does not tend 
to discolour to the same extent as the latter body. 


MANGANESE Borate (MnB,0,) 


Manganese borate is prepared by dissolving commercially pure manganese 
sulphate (iron-free) in hot water and adding this solution to a hot solution of 
borax till no further precipitation takes place. 

As the borate of manganese is somewhat soluble in water only one wash should 
be given ; the white precipitate is then filter pressed and dried. 

Great care must be taken in precipitating and drying borate of manganese, 
otherwise the resultant product is dark coloured instead of being perfectly white. 
Manganese borate when carefully prepared is a white fine light powder, which 
readily dissolves in linseed or wood oil, etc., at about 300° F., producing pale oils 
which dry readily. 

It is largely used as a drier both on account of its excellent drying properties 
and also on account of the fact that it does not discolour the oil to anything like 
the same extent as the other manganese compounds. For this reason it is almost 
exclusively used as a drier in the preparation of pale drying oils and varnishes, 
and also as a constituent of the patent dry or paste zinc white driers, which are 
employed as driers for white paints and enamels. 

The exact composition of pure manganese borate is rather difficult to arrive 
at, because of the fact that when the precipitated borate is washed it continually 
loses boric acid. If repeatedly washed the product in drying out turns brown 
owing to the separation of manganese oxide. 

Commercial pure borate of manganese is a white powder which should contain 
about 19 per cent. of manganese (Mn) and be practically free from alkali. 
Unfortunately large quantities of borate of manganese are put on to the market 
which are heavily adulterated with calcium sulphate (terra alba). 

As the value of a borate of manganese is dependent not alone on its whiteness 
but on the amount of manganese it contains, all samples which on analysis contain 
less than 17-18 per cent. of manganese (Mn) should be rejected (for analysis see 
page 122, under Manganese). 


244 THE CHEMISTRY OF PAINTS 
MANGANESE HyDROXIDE (Mn(OH,)) 


(Brown Oxide of Manganese.) 


Manganese hydrate is prepared by adding a weak solution of caustic soda 
to a solution of manganese chloride or sulphate. The whitish precipitate which 
first forms readily turns brown and is well washed to remove any excess of alkali ; 
it is then filter pressed and dried at a low temperature. 

Manganese hydrate is a darkish brown powder which owing to its greater 
solubility and non-darkening properties is largely used as a drier in the boiling 
of oils and the manufacture of varnishes in place of black oxide of manganese. _ 

Burnt umber which has been prepared by gently roasting raw umber till all 
the moisture has been driven off contains brown oxide of manganese and was 
formerly extensively used in the preparation of boiled oil and varnishes. Its 
place in recent years, however, has been taken by the more active chemically 
prepared driers. 


MANGANESE AcETATE (Mn(C,H,0,),) 


This salt is manufactured by boiling a solution of manganese sulphate with 
acetate of lime. It is a pinkish crystalline body, which on adding to hot oils or 
varnishes readily decomposes, giving off acetic acid whilst the manganese goes into 
solution. It is used to a small extent as a drier, chiefly in the preparation of 
manganese resinates and linoleates. 


MANGANESE CHLORIDE (Mn(Cl,), 4H,0 


Manganous chloride is the final product in all cases where the oxide or carbonate 
of manganese is treated with hydrochloric acid. It is a pink crystalline salt which 
readily dissolves in water and is used as a drying agent in patent driers and in 
the preparation of other manganese driers. 


MANGANESE LINOLEATES, TUNGATES AND RESINATES 


These may be prepared either by precipitation in the same way as the lead 
compounds, using manganese sulphate or chloride as the precipitating agents, or 
else by fusion, cooking manganese acetate into the hot oils or rosin. 

Manganese linoleate (precipitated or fused) usually contains about 6 per cent. 
of manganese; manganese resinate (fused) about 4 per cent., precipitated as a 
tule about 8 per cent. 

The manganese compounds are considerably more powerful driers than the 
lead compounds, and on this account are used in amounts of about 0-5 per cent. 
to 1 per cent., whereas in the case of lead a larger quantity is necessary to obtain 
the same drying effect. The great objection to the use of manganese driers, 
however, is the darkening action which they exert on the oils in which they are 
dissolved. 

Resinates or linoleates of manganese and lead used together have more powerful 


DRIERS OR SICCATIVES 245 


drying properties than either of them used alone; hence it is usual to employ the 
combined resinates or linoleates in the proportion of about 4 parts of lead to 1 part 
of manganese to obtain the best drying effect. 


COBALT DRIERS 


CoBALT ACETATE 


This is prepared by dissolving cobalt oxide in acetic acid. It is a pinkish 
coloured crystalline salt which is largely used at the present time as a drier and 
also in the preparation of cobalt resinates and linoleates by fusion. 

It contains usually 23 to 24 per cent. of metallic cobalt (Co), sometimes 
27 per cent. to 28 per cent. 

CoBALt RESINATE 


This compound is prepared by cooking cobalt acetate with resin at about 
400° F. The best qualities generally contain from 14 to 2 per cent. cobalt. 

It is a very powerful drier, being far superior to lead or manganese resinate, 
and on this account is very largely used in the preparation of terebines and as a 
drier for oils and varnishes. 

CoBaLtt LINOLEATE 


This is prepared by saponifying linseed oil with caustic soda, then adding a 
dilute solution of cobalt chloride. The cobalt linoleate thus precipitated is well 
washed and dried at a low temperature. 

Cobalt linoleate as usually sold is a dark red sticky substance which contains 
about 6 per cent. of cobalt. It readily dissolves in turpentine, white spirit, oils, 
etc., and is very largely used as a drier. 

By reason of its very powerful drying properties only very small quantities 
are required, from 0-25 to 0-5 per cent. being sufficient to dry off an oil or varnish 
in about eight hours. 

The cobalt driers are the most powerful driers known, and at the present time 
are coming more and more into favour and gradually taking the place of the older 
lead and manganese driers. They also possess the unique property of bleaching 
out in the sunlight, which makes them especially valuable as drying agents for 
white enamels and pale varnishes. 

When added to varnishes they do not cause any “footing out” such as is 
obtained when lead or manganese driers are used. 


VANADIUM DRIERS 


According to Rhodes & Chen,! vanadium driers are only slightly less efficient 
than cobalt driers. Oils containing vanadium driers dry about twice as rapidly 
as do oils containing an equivalent amount of manganese drier, and almost five times 
as rapidly as oils containing an equivalent amount of lead drier. Unfortunately, 
however, oils treated with vanadium driers are found to be intensely dark in colour. 
In effective amount the vanadium gives to the oil so dark a colour that its use would 


1 U.S. Paint Manufacturers’ Association Circular, 149. 


246 THE CHEMISTRY OF PAINTS 


have to be confined to dark coloured paints. The cost of the preparations, moreover, 
is greater than the cost of cobalt driers, which are really more effective and of very 
much lighter colour. 

The vanadium compounds which may be used as driers are vanadium resinate 
and linoleate, and are prepared by dissolving ammonium vanadate either in rosin or 
in linseed oil at a temperature of about 300° C. 


TEREBINE (Liguip Drier, Japan DRIER) 


Terebine} is a concentrated liquid drier commonly called in America Japan 
drier, which is largely used as a convenient form of drier to add to liquid paints and 
varnishes in order to increase their drying properties. 

Originally terebine was made by running kauri gum into linseed oil till all 
taken up, then cooking in a large amount of red lead, litharge, and manganese 
dioxide till bright, and then thinning out with spirits of turpentine to a thin 
consistency. 

This preparation on drying out gives a hard, tough, lustrous film, and has 
excellent drying properties. Moreover, it can be mixed in any proportion with 
white lead or zinc oxide without causing any “ livering ” or thickening. 

At the present time terebines are made by heating the oxides of lead and 
manganese or borate of manganese with linseed oil or rosin, or mixtures of linseed 
oil and rosin, at a temperature of about 500° F. till solution takes place and a hard 
mass is produced, and thinning down with turpentine, white spirit, or mixtures of 
both, to a thin consistency. 

The terebine is tanked and left for a few weeks to brighten, and is then ready 
for use. 

The product thus produced is a dark red coloured thin bright liquid, which 
has powerful drying properties. It consists of a solution in turpentine or white 
spirit of lead linoleate, lead resinate, manganese linoleate, manganese resinate, or 
mixtures of these compounds. 

Sometimes, in addition to lead and manganese compounds, compounds of cobalt 
are used, especially in the preparation of very pale terebines. 

A good quality of terebine (liquid drier) should conform to the following 
specification :— 

Specification for Terebine (Liquid Drier) 


1. The terebine must be of a clear, transparent, mobile liquid, sweet in odour, 
and free from any suspended matter or deposit. 

2. It should contain about 70-75 per cent. of volatile matter consisting of 
turpentine or white spirit, or a mixture of these. 

3. When the terebine is poured on to glass, in a vertical position, it should dry 
off in not more than two hours at room temperature, giving a tough, glossy, and 
clear film. 

4. When thoroughly mixed with raw linseed oil at the ordinary temperature, © 


1 Terebine must not be confused with terebene, which is an entirely different body (see p. 203). 


DRIERS OR SICCATIVES 247 


in proportions of 10 per cent. by volume of terebine to 90 per cent. by volume 
of raw linseed oil, and allowed to stand for six hours, no separation should occur 
nor any deposit be formed. 

5. When the above mixture is flowed on to glass, placed nearly vertical, the film 
shall dry off hard at ordinary room temperatures in not more than eighteen hours. 

6. When the terebine is mixed with an equal volume of white spirit, a clear 
solution shall result without residue on standing one hour. 

7. The flash point (close test) must not be below 80° F. 

8. When the terebine is mixed with white lead or zinc oxide liquid paints, no 
curdling or “ livering” up must take place. 


CONCENTRATED DRIERS 


These are made by heating linseed oil or rosin to about 300° C. and dissolving 
in the oxides of lead, manganese or cobalt, or mixtures of these. 

They can also be made by the precipitation process by adding solutions of 
manganese, cobalt and lead salts to solutions of rosin or linseed oil soaps, as described 
under Lead, Cobalt and Manganese Linoleate or Resinate. 

Concentrated driers come on to the market in the form of a dark, thick, viscous 
mass, or in the case of the resinates, as dark, brittle, solid lumps. They are largely 
used in the manufacture of oil varnishes and in oil boiling. 

Ordinarily they contain the following proportions of lead and manganese, or 
cobalt :— 


Lead and Manganese 


Linoleate, precipitated .  .. : . 12 per cent. Pb, 3 per cent. Mn 
ee fused : ; ; : te ele % Pb, 3 ts Mn 

Resinate, fused . ; ; : BeeLO * Pb, 3 ve odin 
if precipitated . , : ticle - Pb, 5 Soe Ne 

Mixed resinate and linoleate . : eke es Pb, 3 ee et Bs 

Cobalt 
Cobalt resinate : : : : . 2 per cent. Co. 
Cobalt linoleate and resinate . ; ia és Co. 


DRIERS GROUND IN OIL OR PASTE DRIERS 


Paste driers are largely used in the paint trade as a handy form in which driers 
may be added to paste or liquid paints to increase their drying properties. 

They are made by grinding together suitable proportions of barytes, whiting, 
white lead, sugar of lead, and manganese acetate or chloride in boiled or raw oil. 
The barytes and whiting simply act as diluents, and, of course, exert no drying action 
on the paints. 

When mixed in suitable proportions—about 7 lbs. to 1 cwt. of paint—to a 


R 


248 THE CHEMISTRY OF PAINTS 


white paint they should mix readily without causing any thickening of the paint, 
and should dry off the paint when it is applied in about twelve hours without any 
discoloration. 

SPECIFICATION FOR DRIERS GROUND IN OIL 


The driers, free from oil, must contain suitable lead compounds equivalent to 
not less than 5 per cent. of lead monoxide (PbO), together with suitable manganese 
compounds equivalent to not less than | per cent. of manganese dioxide (MnQ,). 

The suitability of the lead and manganese compounds will be determined by 
the following drying test :—A thin film of the driers, after thoroughly mixing with an 
equal part of linseed oil of good quality, must dry to the touch in not more than six 
hours when exposed in a dry atmosphere at a temperature of approximately 60° F. 
The composition of the driers must be uniform. 


Dry Driers, FrencH Driers, Zumatic Drirrs, Zinc Driers 


Dry driers are made by grinding zinc white, manganese borate and whiting 
together in suitable proportions. They are sold in the form of a dry white powder, 
and are used for adding to zinc paints, which they should cause to dry off hard 
without any discoloration. 

Compounds of zinc, calctum and aluminium, as the oxides or resinates, etc., are 
used as driers in combination with litharge and manganese borate. These bodies 
are really hardening or neutralising agents, as their drying properties are very small. 


ANALYSES OF TEREBINES, Liqguip DRIERS AND CONCENTRATED DRIERS 


Estimation of the Volatile Spirit gms. of the terebine are evaporated to 
dryness in a sand bath till no more spirit is evolved. Loss of weight equals the 
amount of volatile matter present. 

If an analysis of the thinners is required, then distil off 200 c.c., collect dis- 
tillate ; and test by fractional distillation (see page 198). 

Rosin, by the Liebermann-Storch reaction (see page 162). 

Lead.—Take 25 gms. of the liquid drier. Remove volatile on the water bath 
and ignite gently, then strongly. Add hydrochloric acid to ash. Filter and wash 
with boiling water. Transfer to 6-in. basin and evaporate to small volume. 
Wash into a beaker and add 200 c.c. of hot distilled water, and pass in sulphuretted 
hydrogen. 

Filter, and without washing transfer to a 3-in. basin and add 25 cc. of 
water and a little nitric acid. Cover dish and heat to gentle boil. Filter and wash 
thoroughly. 

To filtrate and washings add 15 ¢.c. alcohol and dilute sulphuric acid. Stand 
for two hours with frequent agitations. 

Filter through ashless paper, well wash with a mixture of alcohol and water, 
dry and ignite. Cool and weigh. . 

Add two or three drops of nitric acid and ignite. Cool and add three drops of 
sulphuric acid. Ignite and weigh. Equals PbSQ,, calculate to Pb. 


DRIERS OR SICCATIVES 249 


Manganese.—Take filtrate from H,S. Evaporate to dryness on a water bath. 
Add a few drops of sulphuric acid, cover basin, and heat gently on a sand bath until 
sulphuric acid fumes cease to come off. This removes the hydrochloric acid. Cool 
and add 40 c.c. of water, and boil. 

Add paste of zinc oxide (pure) and water in small portions at a time. The 
zinc oxide precipitates any iron and neutralises the free sulphuric acid. 

A small quantity of zinc oxide should remain at the bottom of the dish. Filter 
and wash. 

To the filtrate add 1 or 2 gms. of sodium acetate and heat to nearly 
boiling. If a good deal of iron is present some may come down at this stage; 
filter off. 

Add slight excess of bromine water and boil cautiously. The manganese is 
precipitated as manganese dioxide (MnO,). Filter, wash and ignite and weigh. 
Equals Mn,0,. Calculate to Mn. 

Note——The above method is also applicable for the estimation of lead and 
manganese in varnishes. 

An alternative method which gives good -results is to extract the driers from 
the terebines, etc., by shaking them in a flask with an equal volume of warm dilute 
hydrochloric acid for about one hour. 

The mixture is then poured into a separating funnel, and the aqueous acid layer, 
which should contain all the metals present in the medium in solution, is drawn off 
into a porcelain evaporating dish. The oil portion is washed twice with warm 
water, adding the washing to the porcelain dish, and evaporating to dryness. The 
residue consists of the chlorides of all the metals that may be present in the terebine. 

The other metals that may be present in a liquid drier (or in a varnish) besides 
lead and manganese are as follows :— 


1. Cobalt. As a general rule if a cobalt salt has been used as the active 
ingredient the compounds of lead and manganese are absent. 

2. Calcium used in the form of lime as a hardening agent for rosin. 

3. Alumina in the form of aluminium oleate or linoleate to thicken or body up 
the oils. 

4. Copper if the medium has been prepared in a copper varnish pot. 

5. Iron if the medium has been prepared in an iron varnish pot. 


Estimation of Cobalt 


The cobalt is estimated after the removal of the lead manganese (iron and zinc) 
by precipitating with ammonia and ammonium sulphide as cobaltous sulphide ; 
dissolving this precipitate in nitric acid, adding H,SO,, taking down nearly to dryness, 
then diluting with water, making almost neutral with ammonia, and precipitating 
with a boiling hot concentrated solution of ammonium hydrogen phosphate. 

The precipitate is washed, dried and weighed as CoONH,PO,. The other metals, 
such as iron, copper, zinc, alumina and calcium, are estimated if required by the 
usual methods of analysis, which need not be described in detail. 


250 THE CHEMISTRY OF PAINTS 


Cobalt Resinate, Cobalt Linoleate, Cobalt Acetate, etc. 


The percentage of metallic cobalt present in concentrated or solid cobalt driers 
may be estimated as follows :— 

Ash 1 gm. of the sample in a crucible. Dissolve in hydrochloric acid and 
filter. Add 5 c.c. sulphuric acid and evaporate to dryness in a porcelain evaporating 
dish and weigh as cobalt sulphate. Calculate to metallic cobalt. 

An alternative method consists in precipitating the cobalt as hydroxide, drying 
the precipitate, and igniting in a current of hydrogen gas, and weighing the metallic 
cobalt thus produced. 


CHAPTER XXI 


BRUNSWICK BLACKS, BLACK JAPANS AND STOVING 
BLACKS 


THE manufacture of bituminous coatings for the protection of iron and stone work 
from the action of moisture, and also for production of matt or highly lustrous 
black surfaces in coach work, is an important branch of the varnish industry. 

The range of black varnishes manufactured is very large, and their composition 
and properties as regards toughness and elasticity and time of drying varies 
greatly according to the purpose for which they are intended to be used. 

They may dry off at the ordinary temperature in a few minutes, or, on the 
other hand, high stoving temperatures maintained over a period of from two to 
three hours may be necessary before the desired hardness of finish is attained. 

These black varnishes are prepared so that in drying off they produce flat, 
egg-shell gloss, or high gloss finishes. The raw materials mainly used in the 
manufacture of black varnishes are :— 

(1) Natural asphaltum or bitumen, Gilsonite, Manjak. 

(2) Artificial pitches such as— 


Bone pitches. 
Coal tar pitches. 
Stearin pitches. 
Petroleum pitches. 
Wood tar pitches, Waza pitch, rosin pitch, etc. 
(3) Varnish gums. 
(1) AsPHALTUM 


Natural asphalt or bitumen is imported from various places. It occurs in 
almost inexhaustible quantity in the great asphalt lake in the island of Trinidad, 
as also in North America, Mexico, Cuba, Syria, etc. It is a blackish brown, lustrous 
and brittle solid, breaking with a conchoidal fracture. Its specific gravity varies 
from 1-07 to 1-17. 

Asphaltum, the best variety of which is known as Manjak, melts at about 
100° C., giving off a thick brownish vapour with a nasty characteristic smell. On 
ignition it burns with a bright smoky flame, leaving a little ash. It is soluble in 
turpentine, benzol, carbon disulphide and chloroform. 

Asphaltum is generally considered to be a solid polymerised product of 
petroleum. 

251 


252 THE CHEMISTRY OF PAINTS 


Gilsonite is a hard, lustrous, black bitumen having a specific gravity of about 
1-04 and melts at about 300° F. 

It is not equal in staining properties to Manjak. 

The genuine asphaltums have a fixed carbon content of about 15 per cent. 
to 20 per cent., and are quite unsaponifiable. 


(2) ARTIFICIAL PITCHES 


Various artificial pitches, such as coal tar pitch, bone pitch, stearin pitch, 
petroleum pitch, etc., are used also either alone or in conjunction with asphaltum 
for the manufacture of black varnishes. These artificial pitches vary considerably 
as regards their properties, e.g. bone pitch is a very dense black brittle product, 
and is used chiefly on account of its blackness with a softer pitch, such, for instance, 
as stearin pitch. 

Petroleum pitches vary in consistency from solid to semi-liquid, and are 
employed chiefly in the manufacture of the cheaper black varnishes. 


(3) VaRNiIsH GUMS 


Various copal gums in combination with linseed oil are used in the manufacture 
of high-class black Japans to impart lustre and durability to these products. In 
the case of the cheaper quick-drying asphaltum varnishes common rosin is also used 
to increase their lustre, but this is not looked on with favour on account of its 
tendency to make the coating brittle. 


Brunswick BLack 


This asphaltum black varnish is very largely used for coating iron work in 
order to protect the metal from rusting and to give a high lustrous black finish. 
It may be made according to the following general formule (Livache) :— 


1 2 
Asphaltum" ; » 2 parts Asphaltum , ; » I part 
Spirits of turpentine . » oe, Boiled linseed oil ‘ . 3-6 parts 


Spirits of turpentine . » 24 ,, 


Common Biack VARNISH 


Cheap black varnish for wood and iron work for common outside use consists 
of coal tar pitch dissolved in heavy coal tar naphtha; sometimes a mixture of 
creosote oil and naphtha is used. It dries in about four to sixteen hours, 
according to the purpose for which it is intended, and is an excellent protective 
coating against all weathering influences. 


ExTRA QUICK-DRYING BLACK VARNISH 


These varnishes can be made to dry off in about 4 to 1 hour, and are prepared 
by dissolving asphaltum in low flash spirit such as benzol, benzine or shale spirit. 


BLACK VARNISHES 253 


Buack JAPANS 


Black Japans are used mainly in high-class coach work, and are high-grade 
asphaltum varnishes to which a proportion of hard drying copal varnish has been 
added to impart lustre and durability. 

They should dry off hard in a few hours and when varnished over should not 
show any “ greening ”’ effect. 

The asphaltum used in this class of varnishes should be of the best quality, 
hard and lustrous, and of as dense a black as possible. Sweated pitches such as Waza 
pitch are also used, and a little Prussian blue is usually added to increase the 
blackness of the finished Japan. 

The following formule will give a general idea as to the way in which these 
black Japans may be prepared. 


1 2 

Asphaltum . ; . 50 lbs. Asphaltum : : . 10 lbs. 

Linseed oil . ‘ . 10 gals. Sweated Waza pitch . ma AO es 

Litharge ; ; . 4 Ibs. Boiled oil . : : . gals. 

Red lead ’ . et Ra 5 Red lead . ; ‘ ;  4ojbs. 

Hard animi varnish . 5 gals. Hard carriage varnish . 10 gals. 

Turpentine . : . 30 gals. Turpentine : ; ay ey eae 
Prussian blue. ; . 3 028. 


The asphaltum, etc., is melted up in a large iron pot with the linseed oil, and 
the driers cooked in till a portion taken out forms a very hard mass. The pot is 
allowed to cool sufficiently and then thinned down to the right consistency with 
spirits of turpentine. The varnish is finally stirred well in and the Japan strained 
and tanked. 


Stovine Biacks or Baxkine JAPANS 


This class of goods is largely used in the cycle and bedstead trades, and is 
usually applied either by dipping or spraying. 

The coated articles are stoved at temperatures varying from 150-400° F., 
according to the particular nature of the Japan used. 

The Japans after stoving form very hard, tough and exceedingly durable 
coatings on the metal objects on which they are applied. They are manufactured 
by cooking linseed oil with litharge, red lead, and black oxide of manganese till it 
is oxidised to almost a solid mass (lead oil). Stearin pitch, and a little bone 
pitch, to increase the blackness of the finished black, are next added to the hot oil 
mass, and thoroughly cooked until all are amalgamated. The black is then thinned 
down to the right consistency with kerosine, strained and tanked till all impurities 
have settled out. 


254 THE CHEMISTRY OF PAINTS 


Fiat Dryinc Buack JAPANS 


Black drying Japans, either stoving or air drying, are prepared so as to give 
a matt or egg-shell finish. They are made by adding vegetable black to the 
ordinary black Japans in sufficient quantity to give the desired finish, enough 
volatile thinner being added to reduce the product to good working consistency. 


Analysis of Black Japans 


The analysis of a black Japan so as to differentiate the various constituents, 
together with their percentages, is not practicable. 

It is, however, quite sufficient if the Japan under examination is compared 
with various other standard Japans as to its working properties, finish, time of 
drying, etc., as by this means comparative results may be obtained which enable 
it to be identified and related to the class to which it belongs. 

Also no general specification can be given for these black Japans, as they vary 
so much according to the purposes for which they are to be employed. 


BIBLIOGRAPHY 


Handbuch der Farbenfabrikation. Von Georg Zerr und Dr R. Rubencamp, (8rd 
Edition, Union Deutsche Verlagsgesellschaft, Berlin.) 

’ Painters’ Colours, Oils and Varnishes. 5th Edition. By C.H. Hurst. (Griffin & Co., 1913.) 
The Manufacture of Paint. By J. Cruickshank Smith. (Scott, Greenwood & Son.) 
Paint and Colour Mixing. By Arthur Seymour Jennings. (E. & F. N. Spon, Ltd., London.) 
Analysis of Paint Vehicles, Japans and Varnishes. By Clifford Dyer Holley. (John 

Wiley & Sons, Inc., New York, 1920.) 

Analysis of Paint and Varnish Products. By Clifford Dyer Holley. (John Wiley & Sons, 
New York.) 

Various Points in the Manufacture of Lake and Pigment Colours. By J. B. Shaw. 
(Journal of the O. and C. C. Assoc., April 1920.) 

Iron-corrosion, Anti-fouling and Anti-corrosive Paints. By Louis Edgar Andes. (Scott, 
Greenwood & Son.) 

The Analysis and Valuation of Paints, Varnishes and Enamels. By A. de Waele. 
(Journal of the O. and C. C. Assoc., April 1920.) 

Fineness and Texture of Pigments. H. A. Gardner. (Educational Bureau, Washington, 
Circular No. 90, March 1920.) 

Paint a Plastic Material and not a Viscous Liquid. Bingham and Green. (American 
Soc. for Testing Materials, 22nd Annual Meeting, June 1919.) 

Technology of Paint and Varnish. By Sabin. (John Wiley & Sons.) 

The Chemistry of Paints and Paint Vehicles. By Hall. 

The Chemistry of Paints and Painting. By A. H. Church. (Seeley & Co., Ltd,. London.) 

The Chemistry of Pigments. By EH. J. Parry and J. H. Coste. (Scott, Greenwood & Son.) 

The Chemistry of Linseed Oil. By J. Newton Friend. (Gurney & Jackson, 1917.) 

German Varnish Making. By Prof. Max Bottler, translated with Notes on American 
Varnish and Paint Manufacture by Aloah Horton Sabin. (John Wiley & Sons, 
New York.) 

Casein: Its Preparation and Technical Utilisation. By Robert Scherer. (3rd English 
Edition, 1921, revised and enlarged by H. B. Stocks.) (Scott, Greenwood & Son, 
London.) 

Manufacture of Varnishes and Kindred Industries. Livache. 

Bestimmung von Teerfarbstoffen in Farblacken. Von Georg Zerr. (Union Deutsche 
Verlagsgesellschaft, Berlin, 1922.) 

Chemie der organischen Farbstoffen. Von Prof. Dr Rudolf Nietzki. (Springer, Berlin.) 

Die Anilinfarben und ihre Fabrikation. Von Dr K. Heumann, fortgesetz von Dr Paul 
Friedlander. (Vieweg & Sohn.) 

Die neuern Farbstoffe der Pigmentfarbenindustrie. Von Dr C. Staeble. (Berlin.) 

Analysis of Oil Varnishes. (Proc. Am. Soc. for Test. Mat. 8, 1908.) 

Evaluation of White Pigments, with Special Reference to Antimony Oxide. By H. E. 
Clarke. (Journal of the Oil and Colour Chemists’ Assoc., vol. iv., Jan. 1921.) 

255 


256 THE CHEMISTRY OF PAINTS 


Titanium White: Its Production, Properties and Use. (Journal of the Oil and Colour 
Chemists’ Assoc., 1921.) 

Lacquer Industry of Japan. J.J. Quinn. (British Consular Reports, 188.) 

Polymerised Drying Oils. (J. Soc. Chem. Ind., 1915.) 

A Contribution to the Analysis of Oil Varnishes. Wolff. (Farben Zeitung, 1916.) 

Analysis of Oil Varnishes. MclIlhiney. (Proc. Am. Soc. for Test. Mat. 8, p. 596, 1908.) 

Die Chemie der austrocknenden Oele. By Mulder. (Berlin, 1867.) 

Rubber Seed Oil and a Method of producing Glycerides from Fatty Acids. H. A. Gardner. 
(Paint Manufacturers’ Assoc. of the U.S., Circular No. 118.) 

Carbon Black: Its Properties and Uses. By G. St J. Perrott and Reinhardt Thiessen. 
(Journal Ind. and Eng. Chem., xii. 324, 1920.) 


Fineness and Texture of Pigments. H. A. Gardner. (Educational Bureau, Washington, 
Circular No. 90, March 1920.) 

Determination of Volatile Thinners in Oil Varnishes. De Waele and F.Smith. (Analyst, 
1917, 42, p. 170.) 

Analysis of Resins, Balsams and Gum Resins. Dietrich. (1901.) 

Oxidation of Oils. Ingle. (J. Soc. Chem. Ind., p. 639, 1913.) 

Shellac. By A. F. Suter. (Jour. Royal Soc. Arts, 57, 660.) 

Nitrocellulose Industry. By E.C. Worden. 2 vols. (1911.) 

Testing American Aeroplane Varnish. By C. Webb. (Paint, Oil and Drug Review, 
Chicago, May 1919.) 

Turpentine: Its Sources, Properties and Uses. (United States Department of Agriculture, 
Bulletin No. 898.) 

Varnishes from Wood Oil and Rosin. (O. and C. Trades Journal, July 1917.) 

Pyroxyline. G. Lunge. (Z. Angew. Chem., xxix., 2051-58). 

The Analysis of Prussian Blue. Parry and Coste. (The Analyst, xxi. 225-230. 1896.) 

White Lead. W. A. Davis and C. A. Klein. (J. Soc. Chem. Ind., xxvi. 848.) 

Technologie der Fette und Ole. By Gustav Heiter. (Berlin, 1921.) 

Die Chemie der trocknenden Ole. By Dr Fahrion. (Berlin, 1911.) 

Technical Handbook of Oils, Fats and Waxes. By Percival J. Fryer and Frank H.\ Weston. 
(Cambridge University Press.) 

The Testing of Chemical Reagents for Purity. Dr G. Krauch. Translated by J.¥A. 
Wilhamson and L. W. Dupré. (Maclaren & Sons, London.) 

Chemical Analysis of Oils, Fats and Waxes. By Dr J. Lewkowitsch. (Macmillan’& Co.) 

The Manufacture of Lake Pigments from Artificial Colours. By Francis H. Jenninson. 
2nd Edition. (Scott, Greenwood & Son.) 

The Manufacture of Earth Colours. By Josef Bersch. (Scott, Greenwood?& Son.) 

A Practical Treatise of the Manufacture of Colours for Painting. Revised by M. F. 
Malepeyre, translated by A. A. Fesquet. (Philadelphia, 1874.) 


Air Ministry Cellulose Acetate Dope (3 D100). (British Standard and Air Board Speci- 
fications for Aircraft Materials, Ist Nov. 1922.) 

Nitro-cellulose Dope (D102). (British Standard and Air Board Spec., etc.) 

Properties of Aeroplane Dope. (British Standard and Air Board Spec., etc.) 

Handbuch der Lack- und Firnisindustrie von Seeligmann und Zicke, Dritte Auflage. 
(Berlin, 1923.) 

Die Anstrichfarben und ihre Bindemittel im Farbenhandel. Von W. Antony. (Berlin, 
1923.) 


Aluminium 


Antimony . 


Argon 
Arsenic 
Barium 
Bismuth 
Boron 
Bromine 
Cadmium 
Cesium 
Calcium 
Carbon 
Cerium 


Chlorine 


Chromium . 


Cobalt 
Columbium 
Copper 
Dysprosium 
Erbium 


Kuropium . 


Fluorine 
Gadolinium 
Gallium 
Germanium 
Glucinum 
Gold . 
Helium 
Holmium 


Hydrogen . 


Indium 
Iodine 
Tridium 
Iron . 
Krypton 
Lanthanum 
Lead 
Lithium 
Lutecium 
Magnesium 


Manganese . 


Mercury 


Symbol. 


Al 
Sb 


APPENDIX 


Atomic 
Weight. 
27-1 

120-2 
39-9 
74-96 

137-37 

208-0 
10-9 
79-92 

112-40 

132-81 
40-07 
12-005 

140-25 
35-46 
52-0 
58-97 
93-1 
63-57 

162°5 


1921 
INTERNATIONAL Atomic WEIGHTS 


257 


Symbol. 


Molybdenum ‘ - Mo 
Neodymium : « Nd 


Neon . : Z «. Ne 
Nickel : : . Ni 
Niton (radium emanation) Nt 
Nitrogen ; oN. 

Osmium . ; es 
Oxygen : : eas 

Palladium . : Bee a! 
Phosphorus : fd 

Platinum . : eet 
Potassium . : by Ke 

Praseodymium . Roalg: 
Radium : ; ee 
Rhodium . j «.. Rh 
Rubidium . ‘ ee a. 
Ruthenium ; an Ett 
Samarium . : ae 
Scandium . ; » Be 
Selenium . : . Se 
Silicon . ; St 

Silver : : . Ag 
Sodium : ; . Na 
Strontium . ; .* Sr 
Sulphur. ; as, 

Tantalum . 3 di 
Tellerium . : . Te 
Terbium . 3 BO ide) 
Thallium . : end i 
Thorium . : rae O 
Thulrgm 2 i . Tm 
Tin Ge: ; : ee IE 
Titanium . : peut 

Tungsten . : reas 
Uranium . : 4 -U 

Vanadium . ‘ haar" 

Xenon ; : . x&e 
Ytterbium(Neoytterbium) Yb 
Yttrium e e e Yt 
Zinc . F é Pay si) 
Zirconium . a eo A 


Atomic 
Weight. 


96.0 
144-3 
20-2 
58-68 
222-4 
14-008 
190-9 
16-00 
106-7 
31-04 
195-2 
39-10 
140-9 
226-0 
102-9 
85-45 
101-7 
150-4 
45-1 
79-2 
28-3 
107-88 
23-00 
87-63 
32-06 
181-5 
127-5 
159-2 
204-0 
232-15 
168-5 
118-7 
48-1 
184-0 
238-2 
51-0 
130-2 
173-5 
89-33 
65-37 
90-6 


258 THE CHEMISTRY OF PAINTS 


WEIGHTS AND MEASURES 


MEASURES OF WEIGHT 


Grains. Grams. Ozs. Lbs. Cwt. 
1 064799 ae -000143 
15-4326 1 03527 002204 RA 
437-5 28-3495 1 0625 000558 
7000 453-59 16 I 00893 
50802 -35 1792 112 if 


1 cwt.=50-8024 kg. 1 kg.=2-2046223 lbs. 
1 metric ton=1000 kgs.=2,204-622 lbs.=-9842 imperial ton. 
1 imperial ton=1,016,047 grams=2,240 Ibs.=1-016 metric ton. 


LINEAR MEASURE 


Ins. Ft. Yds. Miles. Cm. Metre. Km. 
1 083 02778 0000158 2-5399978 0254 1-0000254 
12 1 333 0001894 30-47997 -3048 0003048 
36 3 1 000568 91-44 9144 -0009140 
63360 5280 1760 ] 1609315 1609-315 1-609315 
-393701 aie Ag 45 1 iP cia 
39-3701 3:280843 1-093614 te 100 1 ‘001 
1093-61426 *62137 100,000 1000 1 


SeuaRE MEASURE 


1 sq. in. =6-451589 sq. cm. 1 sq. dm.= 15-50006 sq. ins. 
1 sq. ft. =9-29029 sq. dm. 1 sq.m. = 10-7693 sq. ft. 

1 sq. yd. = -836126 sq. m. 1lsq.m. = 1-195992 sq. yds. 
lacre = 4840 sq. yds. lare =119-59921 sq. yds. 
lacre = -40468 hectare lare =  -0247106 acres 


640 acres=1 mile 


Cusic MEASURE 


1 c.c, = -061024 cu. ins. 1 cu. in. =16-38702 cu. cm. (cm?.). 
1 cm. (m?,)=35-31476 cu. ft. 1 cu. ft. =28-31677 cu. dm. (d.m°.). 
lcm = 1-3907954 cu. yds. leu. yd.= -76455285 cu. m. (m*.). 

1 cu, in. of water at 62° F. weighs = -036041 lbs. 

1 35 A * - », 202-286 grains. 

1 ou, ft oc: Se a » 996-458 ozs. 


1 > 29 99 3) ry 62-2786 lbs. 


APPENDIX 259 


MEASURE OF VOLUME 


Cu. cm. Litres. Cu. in. Cu. ft. Fl. oz. Pint. Gallons. 
1 oe 061027 ae 0352 “00176 Hae 
1000 1 61-0349 035216 35-196 1-761 -220096 
16:387 0164 e sé ‘DTT 02885 Fp 
28315-3 28-3153 Ab 1 997-1364 49-8569 6-2321 
28-396 ie 1-7329 «oe 1 Se os 
567-919 -56825 34-659 ae 20 (water) 1 -125 
4545°96 4-54596 277-274 af 160 8 1 


1 c.c.=-282 fl. drams. 


MENSURATION OF REGULAR FIGURES 


Area of a triangle=3 base x height. 

Area of a parallelogram=base X perpendicular height. 

Area of a trapezium=half the sum of the parallel sides xthe 
perpendicular distance between them. B 

Area of a sector A B C of a circular is 4 (arc B C) x(radius)= 
470. r=r?0. Where 0 is the angle of the sector measured in radians. Co 

Volume of pyramid=4 (area of base) x (height) =117/. 

The portion of a pyramid or cone cut off by a plane parallel to the 
base is called a frustrum. 
z Volume of a frustrum of a pyramid B 


=5 (A+ /ABTB), 


where fh is the height and A and B are the areas of the 
two parallel faces. 
If r, and r, are the radii of the two parallel faces of 
a frustrum of a cone, then A=ar,?, B=ar,?, and the volume of a frustrum of a 


| 


cone= ae (727-1 yrot72?). 


Cylinder 


Volume of a cylinder= zr?h. 
Volume of a frustrum of a cylinder maths, 
If ris the internal and R the external radius of a hollow cylinder or 


pipe, the volume is the difference between the volume of the external 
cylinder and that of the internal cavity= 7R?h— a7*h = mh(R*—1°). 





THE CHEMISTRY OF PAINTS 


CoMPARISON OF FAHRENHEIT AND CENTIGRADE THERMOMETERS 


260 

o° Ns 
—10 14 
—5 23 
0 32 
+5 41 
10 50 
15 59 
20 68 
25 17 
30 86 
35 95 
40 104 
45 113 
50 122 

To convert— 


Fe 


131° 


140 
149 
158 
167 
176 
185 
194 
203 
212 
221 
230 


Co 

120 
130 
140 
150 
160 
170 
180 
190 
200 
210 
220 
230 


Rules 


FY 
248 
266 
284 
302 
320 
338 
356 
374 
392 
410 
428 
446 


(Oh 
240 
250 
260 
270 
280 
290 
295 
300 
325 
350 
375 
400 


°F into °C—First subtract 32, then multiply by 5 and divide by 9. 
°F into °R—First subtract 32, then multiply by 4 and divide by 9. 


°C into °F—Multiply by 9, divide by 5, then add 32. 


°C into °R—Multiply by 4 and divide by 5. 
°R into °F—Multiply by 9 and divide by 4, then add 32. 
°R into °C—Multiply by 5 and divide by 4. 


Element. 


Al 


As 


Ba 


Ca 


Fe 


Mg 


To convert 


Al,03 


into 


Als 


FACTORS REQUIRED IN GRAVIMETRIC ANALYSIS 


Ammonia Alum 


Potash Alum 


As,03 


2 
Na,S0,IOH,O 


MeSO, 
PbsO, 
S05 

S 


CaS0,2H,0 


CaCO, 


2Mg0 


Multiplier. 
0-5294 
8-8824 


Fr 

464 
482 
500 
518 
536 
554 
563 
572 
617 
642 
667 
692 


APPENDIX 


Multiplier. 


Weight. 


36-5 gms, per litre. 


0-4839 
0-6387 
0-4366 
1-0733 
0-8658 
0-6826 
0-6406 
0-7355 
1-092 

0-7143 
0-8025 
0-6701 


2 +5372 
0-4667 
8-8068 
3:03 
4-4 
0-8526 


Element. To convert into 
Mg,As,0, As, 
Mg,As,07 . AsO, 
Na Na,SO,10H,O Na,O 
Pb Pb PbO 
PbS Pb 
PbSO, Pb 
PbCrO, Pb 
PbSO, PbO 
PbSO, Pb(NOs)o 
Sb Sb.Ss Sb. 
Zn ZnO Zn. 
Zns Zn 
Addenda 
Al Alumina (Al,03) China Clay 
China Clay Silica (Si0,) 
C CO, White Lead 
Fe Fe Prussian Blue 
N N Me 
Pb PbSO, White Lead 
' STanDARD SOLUTIONS REQUIRED IN VoOLUMETRICAL ANALYSIS 
. Solutions. 
Substance. Formula 
Hydrochloric Acid HCl 
Nitric Acid : HNO, 
Sulphuric Acid . H,SO, 
Caustic Soda NaOH 
Caustic Potash . KOH 
Sodium Carbonate Na,CO, 


Potassium Iodide 3 seg sl Fe 


Oxalic Acid COOH . 
| +2H,O 
COOH 
. Solutions. 
Potassium Ferrocyanide K,Fe(CN),3H,O 
Potassium Cyanide KCN ; : 
Arsenious Oxide As,O3 
N . 
i0 Solutions. 
Potassium Dichromate K,Cr,O, . 
Potassium Permanganate KMnO, . f 
Sodium Thiosulphate . Na,8,0,5H,O . 
Todine : 2 I : : 


Silver Nitrate 


2 . 
AgNO, 


9 2) 


261 


262 


° 


COAIAMAERWHHEHD 


MULTIPLIERS REQUIRED IN VOLUMETRIC ANALYSIS 


Tron (Fe)=56. 
16.c. st KMn0O,, K,Cr,0,4, or Hyposulphite=0-0056 gms. of Fe=0-0072foms.*FeO= 


0-0080 gms. Fe,0z. 
Chlorine (Cl)=35-5. 


1c.c. : AgNO,=0-00355 gms. of Cl=0-005845 gms. NaCl. 
Todine (I)=127 


THE CHEMISTRY OF PAINTS 


1c.c. a Hyposulphite=0-0127. 


1c.c. I Todine=0-0060 gms. Sbh=0-0072 gms. Sb.03. 


Oxalic Acid ( 


lc.c. — 


TWADDELL AND BEAUME DEGREES AND EQuIVALENT SPECIFIC GRAVITIES 


10 


Sp. Gr= 


COOH 
COOH 


KMn0,=0-0063 gms. C,H,0,2H,O=0-0045 gms. C,H,O,. 


2B ws 

18 28-4 
19 30-4 
20 32-4 
21 34:2 
22 36-0 
23 38-0 
24 40 

25 «42 

26 44 

27 «46-2 
28 48-2 
29 50-4 
30 52-6 
31 54:8 
32 «57 

33 59-4 
34 61-6 


“Tw x5 
1+— 7000 





2H,0=126)). 


Sp. Gr. °B ewe 
1-142 35 «64 
1-152 36 66-4 
1-162 37 =669 
1-171 38 71-4 
1-180 39 «74 
1-190 40 76-6 
1-200 41 79-4 
1-210 42 82 
1-220 43 84:8 
1-231 44 87-6 
1-241 45 90-6 
1-252 46 93-6 
1-263 47 96-6 
1-274 48 99-6 
1-285 49 103-0 
1-297 50 106-0 
1-308 

Hydrometers 
°T waddell= 


Sp. Gr. 
1-320 
1-332 
1-345 
1-357 
1-370 
1-383 
1-397 
1-410 
1-424 
1-438 
1-453 
1-468 
1-483 
1-498 
1-515 
1-530 


°Tw. 
109-2 
112-6 
116-0 
119-4 
123-0 
127-0 
130-4 
134-2 
138-2 
142-0 
146-4 
150-6 
155-0 
159-0 
164-0 
168-4 





For liquids denser than water 


°Beaumé=144— 


144 


Sp. Gr. 


For liquids less dense than water. 


°Beaumé= 


144 
Sp. Gr.—134 





(Sp. Gr.—1) x 1000 
5 


Sp. Gr. 
1-546 
1-563 
1-580 
1-597 
1-615 
1-635 
1-652 
1-671 
1-691 
1-710 
1-732 
1-753 
1-775 
1-795 
1-820 
1-842 


Per 
cent. 


Sp. Gr. 
0-9992 
1-0007 
1-0022 
1-0037 
1-0052 
1-0067 
1-0083 
1-0096 
1-0113 
1-0127 
101-0142 
Tt 10157 
12 1-0171 
131-0185 
14 1-0200 
151-0214 
161-0228 


CONDO WD KH © 


APPENDIX 


Tue SPEcrIFIC GRAVITY OF AcETICc Acrip aT 15° C. 


Per 
cent. 


17 


Sp. Gr. 


1-0242 
1-0256 
1-0270 
1-0284 
1-0298 
1-0311 
1-0324 
1-0337 
1-0350 
1-0363 
1-0375 
1-0388 
1-0400 
1-0412 
1-0424 
1-0436 
1-0447 


34 


er 
ere Sp. Gr. 


1-0459 
1-0470 
1-048] 
1-0492 
1-0502 
1-0513 
1-0523 
1-0533 
1-0543 
1-0552 
1-0562 
1-0571 
1-0580 
1-0589 
1-0598 
1-0607 
1-0615 


Per 
cent 


51 


Sp. Gr. 


1-0623 
1-0631 
1-0638 
1-0646 
1-0653 
1-0660 
1-0666 
1-0673 
1-0679 
1-0685 
1-0691 
1-0697 
1-0702 
1-0707 
1-0712 
1-0717 
1-0721 


Per 


cent. 


68 
69 
70 
(a 


eu cr ee 
1-0725 85 

1-0729 86 

1-0733 87 

1-0737 88 

1-0740 89 

1-0742 90 

1-0744 91 

1-0746 92 

1-0747 93 

1-0748 94 

1-0748 95 

1-0748 96 

1-0748 97 

10747 98 
1-0746 99 

10744 100 

1-0742 


263 


Sp. Gr. 


1-0739 
1-0736 
1-0731 
1-0726 
1-0720 
10713 
1-0705 
1-0696 
1-0686 
1-0674 
1-0660 
1-0644 
1-0625 
1-0604 
1-0580 
1-0553 


Note.—The specific gravities above 1-0553 in each case represent two liquids of very 
different strength. 
In order to ascertain whether the acid exceeds the maximum density (78 per cent.) 
or the reverse, it suffices to add a little water ; in the case of stronger acid the specific 
gravity increases, and decreases if the acid is weaker. 


Sp. Gr. 
at 15/4° 


1-005 
1-020 
1-040 
1-060 
1-080 
1-100 
1-120 
1-140 
1-160 
1-180 
1-200 
1-220 
s 


SULPHURIC ACID 


Speciric GRAVITY AND CONCENTRATION OF ITS SOLUTIONS 


H,SO, 
per cent. 
0-83 
3°03 
5-96 
8-77 
11-60 
14-35 
17-01 
19-61 
21-19 
24-76 
27-32 
29-84 


Sp. Gr. 
at 15/4° 


1-240 
1-260 
1-280 
1-300 
1-320 
1-340 
1-360 
1-380 
1-400 
1-420 
1-440 
1-460 


per cent. 


32-28 
34-57 
36-87 
39-19 
41-50 
43-74 
45-88 
48-00 
50-11 
52°15 
54-07 
55-97 


Sp. Gr. 
at 15/4° 


1-480 
1-500 
1-520 
1-540 
1-560 
1-580 
1-600 
1-620 
1-640 
1-660 
1-680 
1-700 


H,S0, 


per cent. 


57°83 
59-70 
61-59 
63-43 
65-08 
66-71 
68-51 
70-32 
11-99 
73-64 
75-42 
(EME 


Sp. Gr. H,SO, 

at 15/4° per cent. 
1-720 78-92 
1-740 80-68 
1-760 82-44 
1-780 84-50 
1-800 86-90 
1-820 90-05 
1827 91-50 
1-834 93-05 
1-839 95-00 
1-8415 97-00 
1-8400 98-70 
1-8385 99-95 


264 THE CHEMISTRY OF PAINTS 


TABLE SHOWING THE STRENGTHS OF Nitric ACID OF 
DIFFERENT DENSITIES 


Sp. Gr. HNO, Sp. Gr. HNO, Sp. Gr. HNO, Sp. Gr. HNO, 
at 15°C. per cent. at 15°C. per cent. at 15°C. per cent. at 15°C. per cent. 
1-020 3°70 1:170 27-88 1-320 50-71 1-470 82-90 
1-030 5-50 1:180 29°38 1-330 52-37 1-480 86-05 
1-040 7:26 1:190 30°88 1:340 54-07 1490 89-60 
1-050 8-99 1:200 32-36 1:350 55:79 1500 94-09 
1:060 10-68 1:210 33-82 1-360 57-57 1502 95-08 
1-070 12°33 1-220 35°28 1-370 59-39 1-504 96-00 
1080 13-95 1-230 36-78 1-380. 61-27 1-506 96°76 
1090 15-53 1:240 ~ 38-29 1:390 63-23 1508 97-50 
1:100 1711 1:250 39-82 1-400 65:30 1510 98-10 
1-110 18-67 1:°260 41°34 1410 67-50 1512 98-53 
1:120 3 =20-23 1270 42-87 1-420 69-80 1514 98-90 
1-130 21-77 1-280 44-4] 1-430 12h 1-516 99-21 
1:140 (23-31 1-290 45-95 1-440 74°68 1518 99-46 
1:150 24-84 1-300 47-49 1450 77-28 1-520 99-67 

1:160 26:36 1-310 49-07 1-460 79-98 


TABLE SHOWING THE STRENGTH OF HyprocHLoric ACID OF 
DIFFERENT DENSITIES 


Sp. Gr. HCl Sp. Gr. HCl Sp. Gr. HCl Sp. Gr. HCl 
at 15°C. per cent. at 15°C. per cent. at 15°C. per cent. at 15°C. per cent. 
1-005 1-15 1055 11-18 1:105 20-97 1-155 30-55 
1-010 2°14 1-060 12:19 Llld. 21-92 1:160 31:52 
1-015 3°12 1-065 13-19 1-115 22-86 1-165 32-49 
1-020 4-13 1070 14-17 1-120 23-82 1170 33-46 
1-025 5-15 1075 15-16 1-125 24-78 1-175 34-42 
1-030 6°15 1080 1615 1-130 25-75 1-180 35:39 
1-035 7:15 1-085 17-13 1-135 26-70 1185 36-31 
1-040 8-16 1090 18-11 1:140 27°66 1-190 3723 
1-045 9-16 1095 19-06 1-145 28-61 1:195 38-16 


1-050 10-17 1:100 20-01 1-150 29-57 1:200 39-11 


APPENDIX 


TABLE GIVING STRENGTHS OF SOLUTIONS oF Caustic SopA AND PoTAsH 
BY THEIR SPECIFIC GRAVITY 


Sp. Gr. 


1-0070 
1-0141 
1-0213 
1-0286 
1-0360 
1-0435 
1-0511 
1-0588 
1-0667 
1-0746 
1-0827 
1-0909 
1-0100 
1:1077 
1-1163 
1-1250 
1-1339 
1-1423 


Per cent. Per cent. 
OH 


NaOH 


0-61 
1-20 
2-00 
2°71 
3°35 
4-00 
4-64 
5-29 
5:87 
6-55 
7°31 
8-00 
8-68 
9-42 
10-06 
10-97 
11-84 
12-64 


per cent. 


0-91 
1-37 
1-84 
2-31 
2-80 
3°29 
3°80 
4-30 
4-80 
5-30 
5-80 
6-30 


0-90 
1-70 
2-60 
3°50 
4-50 
5-60 
6-40 
7-40 
8-20 
9-20 
10-10 
10-90 
12-00 
12-90 
13-80 
14-80 
15-70 
16-50 


Sp. Gr. 


1-1520 
1-1613 
1-1707 
1-1803 
1-1901 
1-2000 
1-2101 
1-2202 
1-2308 
1-2414 
1-2522 
1-2632 
1-2743 
1-2857 
1-2973 
1-3001 
1-3211 
1-3333 


Per cent. Per cent. 
NaOH KOH 


13-55 17-60 
14:37 =—-18-60 
15-13 19-50 
15-91 20-50 
16-77 =—.21-40 
17-67 22-50 
18:58 23-30 
19-58 24-20 
20-59 25-10 
21:42 26-10 
22-64 27-00 
23-67 28-00 
24-81 28-90 
25:80 29-80 
26-83 30-70 
27-80 31-80 
28-83 32-70 
29-93 33-70 


Sp. Gr. 


1-3458 
1-3585 
1-3714 
1-3846 
1-3981 
1-4187 
1-4328 
1-4472 
1-4619 
1-4769 
1-4845 
1-4922 
1-5000 
1-5079 
1-5158 
1-5238 
1-5319 


SPECIFIC GRAVITIES OF AQUEOUS AMMONIA 








Sp. Gr. Sp. Gr. 
5 Pty, fe Sarena J 
6-80 948 13-31 "924 
7°31 946 13-88 “922 
7-82 944 14-46 920 
8-33 942 15-04 918 
8-84 940 15-63 916 
9-37 “938 . 16-22 914 
9-91 936 16-82 912 
10-47 934 17-42 910 
11-03 932 = 18-03 908 
11-59 930 =: 18-63 “906 
12-17 928 19-25 904 
12-74 926 19-86 “902 


- per cent. 


20-49 
21-11 
21-75 
22-38 
23-03 
23-67 
24-33 
24-98 
25-65 
26-31 
26-98 
27-65 


265 
Per cent. Per cent, 
NaOH KOH 
31-22 34-90 
32°47 35-90 
33-69 36-90 
34-96 37-80 
36-25 38-90 
38°13 40-40 
39°39 41-50 
40:75 42-75 
42-12 44-00 
43-66 45-20 
44-38 45-80 
45-27 46-45 
46-15 47-10 
46-87 47-70 
47-60 48-30 
48-8] 48-85 
49:02 49-40 
Sp. Gr. 
15° 0, percent 
900 28-33 
898 29-00 
896 29-69 
894 30-36 
892 31-05 
890 31-75 
888 32:5 
886 33:3 
884 34-1 
882 34-95 
‘880 35-70 


266 THE CHEMISTRY OF PAINTS 


TABLE oF SOLUBILITIES 


Abbreviations :—s. soluble; r.s., readily soluble; s.s., sparingly soluble; i., insoluble. 


Name. 


Alum (Ammonium) 
Alum (Potassium) 
Alum (Sodium) . 


Alumn. Chloride 
» Sulphate 


Ammonium Chloride . 
; Sulphate . 


Barium Chloride 
»  Chromate 
» Sulphate 
» Hydroxide 
Bleaching Powder 
Boric Acid 
Borax : 
Calcium Chloride 
cp Carbonate 
4 Sulphate 
iN Hydroxide 
Copper Acetate . 
» Sulphate 
Chrome Alum 


Ferrous Sulphate 


Ferrous Ammnm. Sulphate . 


Ferric Sulphate . 
Lead Nitrate 

», Chloride 

» Acetate 


», Carbonate Nariel : 
Basic Lead Carbonate (White 


Lead) 


Lead Chromate (Chromes) 


», Sulphate 
» Oxide 


, Letroxide (Red Tan) 


Magnesium Chloride 


A; Sulphate . 


- Carbonate 


Formula. 


Al,(SOq)3 3 (NH4)2504 
+24H,0 
K,80,+-Al,(S0,)s 
+24H,O0 
Alp(SO4)3+NaSOq 
+24H,O 
Al,Cl,(+-12H,0) 
Al,(SO,4)3 ; 18H,O 
NGL. 
(NH,),SO, 
BaCl,, 2H,0 


Na,B,0, ; 10H,0 
CaCl,, 6H,O 
CaCO, 

CaSO, 

Ca(OH), . : 
Cu(C,H30»)2; HO 
Cu8O,5H,O . 
KOr(SOq)o.12H,O 


FeSO,.7H,O 
Fe(NH,)o(804)2 - 
Fe(SO,)3.9H,O . 
Pb(NOs)o 

PbCl, ; 
Pb(CH302)2 
PbCO, a 
2PbCOs, Pb(OH), 


PbCr0, 


Molecular 


Weight. 
904-4 
948 
917 
265-8 
664-8 


53 +38 
132 


Solubility in 100 Parts 


of Water. 
Cold, 20° C. Hot, 100° C. 
13-66 422 
15-13 357 
110-0 rs. 
400 Si 
86-85 TiszZ 
37-28 72:8 
75-4 103°3 
35-7 58-8 
S.S. S.S. 
L 1. 


3:48 90-77 (80°) 


4 34 


7-88 201-43 
74 155 

3°3 8.8) 

0-241 0-217 

0-126 0-060 
10 20 
42-31 203 -32 


Soluble in 6-7 parts 
of cold water 


60 333 
21-6 56-7 (75°) 
r.8. liquefies 
52-3 127 
1-18 3-1 (80°) 
48 70 
i i 
i i 
8 i 
8.8. 8. 
1. he 
ty ls 
200 367 
36-2 738 
i. 13 


Name. 


Manganous Sulphate . 
Mercuric Chloride 
Potassium Chloride 


é Bromide 
a Iodide 
4: Nitrate 
e Sulphate 
a Carbonate . 
ie Chlorate 
he Bromate 
- Chromate . 
2 Dichromate 
e Permanganate 
Silver Nitrate 
Sodium Chloride 
3» Nitrate . 
» Sulphate 


» Carbonate 
» Bicarbonate 
», Phosphate 


»  Sulphite : 

»,  Thiosulphite . 

» Acetate. 
Bichromate 


Stannous Chloride 
Zinc Acetate 
, Carbonate . 
,, Chloride 
», Sulphate 
», Sulphide 


APPENDIX 


Formula. 


NaNO, . : 
Na,SO,.10H,O . 
Na,CO3.10H,O . 
NaHCO, . : 
Na,PHO,.12H,O 
Na,SOz : 
Na,8.0, . : 
NaC,H,0,.3H,0 
Na,Cr,07.2H,0 . 
SnCl,.2H,O 
Zn(CyH30.)2.3H,O 
ZnCO3.7H,0 
ZnCl, 3 
ZnSO,.7H,O 
ZnS . 


Molecular 
Weight. 


151 
271 
74:5 
119 
165-6 
101 
174 
138 
122-5 
167 
194-5 
295 
158 
169-7 
58-5 
85 
322 
286 
84 
358 
126 
158 
136 
299 
225 
237 
143 
136 
287 
97 


267 
Solubility in 100 Parts 
of Water. 
Cold, 20° C. Hot, 100° C. 
66-3 52-9 
7-39 53-96 
34-7 56-6 
64-52 102-0 
144-2 209 
31-2 247 
10:9 126-2 
94-06 153-66 
7-0 60-0 
6-92 49-75 
62-94 79°10 
12-4 94-10 
6-25 Ars 
228-0 940-0 
35-6 39-61 
87-5 180 
19°5 42-5 
92-8 540 
9-6 16-7 (70°) 
9-3 98-8 
25°8 hes 
69-5 192 (60°) 
33 200 
120 433 
271 
I.s8. r.s 
i i 
300 r.S 
135 655 


INDEX 


Abietic Acid, 161 
Acaroid Resins, 173 
Acetic Acid, Specific Gravity of, 263 
Acetone, 211 
Acid Dye-stuffs, 136-139 
Acid Value, 178 
Adjective Dye-stuffs, 145 
Agricultural Paints, 10 
Alcohol, Absolute, 209 
Amyl, 211 
Butyl, 211 
Ethyl, 208-210 
Methyl, 210-211 
Synthetic, 210 
Wood, 210-211 
Alcoholic Varnishes, 232-234 
Alizarine, 135 
Alizarine Lake, 145, 146 
Alpha Naphthylamine Lake, 142 
Aluminium Hydroxide (Alumina), 37, 39, 137 
Paints, 15 
Silicate, 34 
Amber, 169 
Ambre Gris, 169 
American Petroleum, 204, 205 
Turpentine, 195-200 
Ammonia, Specific Gravity, 265 
Amy] Acetate, 213 
Alcohol, 211 
Analysis of American Turpentine, 196-198, 200 
Anti-Fouling Compositions, 12, 13, 14 
Barytes, 29-31 
Black Japans, 254 
Black Pigments, 132 
Boiled Linseed Oil, 186 
Substitute, 186, 187 
Brunswick Blue, 91 
Brunswick Green, 98 
Burnt Sienna, 64 
Burnt Umber, 122, 123 
Carbon Black, 130 
Camphor Oil, 208 
Chromium Oxide Greens, 101 
Concentrated Driers, 248, 249 
Distempers, 20 


. Antimony rage St ae 


Analysis of Iron Oxides, 111-113 
Lakes and Lake Pigments, 146-149 
Lead Chromes, 75, 76 
Lithopone, 55, 56 
Menhaden (Fish) Oil, 191 
Mineral Black, 126 
Ochres, 62, 63 
Oil of Turpentine, 196-198, 200 
Oil Varnishes, 227-231 
Orange Lead, 117 
Paints, 21-24 
Perilla Oil, 190 
Pigments, 151-159 
Portuguese Turpentine, 203 
Prussian Blue, 90 
Raw Linseed Oil, 177-182 

Substitute, 186, 187 
Raw Sienna, 64 
Raw Umber, 122, 123 
Red Lead, 117 
Rosin, 162 
Russian Turpentine, 202 
Shellac, 168 
Soya Bean Oil, 190 
Spirit Varnishes, 236 
Swedish Turpentine, 202 
Terebines (Liquid Driers), 248, 249 
Ultramarine Blue, 84, 85 
Vandyke Brown, 124 
Vermilion, 120 
Walnut Oil, 191 
White Lead, 46, 47 
White Spirit, 206-208 
Wood (Tung) Oil, 188 
Wood Turpentine, 201 
Zinc Chromes, 78 
Zine Green, 100 
Zine Oxide, 50-52 

Anglo-American System, 175 
Press, 176 

Angola Copal, 171 

Animal Black, A3hs*, odds: cus ucet ad Valea 


> | Anirpi, 170° : > ; ; ; > 20 
nek Ant? Cobrodions ‘Paints, 10, 1 se; wh eet sete 


Anti-Fouling Compositions, Il, 12, » 13, 14 


Emerald Green, 104, 105 

Green Earth, 95 5° 3Oxide, 58> 55) > sf - oes 

Hemp Seed Oil, 191 ECE I ae ong 
269 


270 THE CHEMISTRY OF PAINTS 


Antimony White, 58, 59 
Antwerp Blue, 92 
Armstrong, H. E., on White Lead, 39 
Arsenic Orange, 79 
Artificial Pitches, 252 
Asbestos Paints, 20 
Asphaltum, 251 

Atomic Weights, 257 
Augites, 95 

Aureolin, 79 

Autol Red B L, 142 
Azo Dye-stufis, 141-143 


Baeyer, A., on Synthetic Dye-stufis, 135 
Balsams, 161, 163, 164 
Barium Carbonate, 35 
Barium Chrome, 79 
Sulphate, 27 
Barytes, 27, 137 
Air-floated, 28 
Analysis of, 27-31 
English, 29 
Properties and Uses, 29 
Spanish, 29 
Water-floated, 28 
Basic Dye-stufis, 136, 139, 140 
Lead Carbonate, 39 
Sugar of Lead, 239, 241 
Beaumé Hydrometer, 262 
Bean Oil, 189 
Benguela Copal, 171 
Benjamin Gum, 165 
Benzene (Benzol), 214 
Benzine, 203, 205 
Benzoin, 165 
Benzyl, Alcohol, 237 
Berlin Blue, 85 
Beta Naphthol, 142 
Bibliography, 255, 256 
Bitter Almond Green, 135 
Bitumen, 251 
Black Boy Gum, 173 
Japans, 253 
Lake, 135 
Lead, 126 
Oxide of Iron, 126 
Pigments, 125-132 
Analysis of, 132 
Toner, 131 
Varnish, 252 
Black, Bone, 130, 131 
Brunswick, 251-254 
Carbon, 130 
Drop, 131, 132 
Frankfort, 131 
German, 131 
Jet, 181 | 
Lap, 128; 1 29 
‘Vegetable, ‘128, 129 ° 
Vine, 131, 132 
Blanc-fixé, 35 oc ahs - 
Bleached Sheliav; 168; 169. 








Blown Oils, 2, 186 
Blue, Antwerp, 92 
Berlin, 85 
Bremen, 93 
Bronze, 89 
Brunswick, 91 
Celestial, 91 
Chinese, 77, 85-89 
Cobalt, 92, 98 
Copper, 93 
King’s, 93 
Lime, 85 
Milori, 89 
Paris, 85, 89 
Prussian, 85-91 
Steel, 89 
Turnbull’s (Gmelin’s), 92 
Ultramarine, 80-85 
Blue Lacquer, 235 
Body Varnish, 217, 222 
Boiled Linseed Oil, 183, 186 
Substitutes, 186, 187 
Boiled Soya Bean Oil, 189 
Bone Black, 130, 131 
Bone Oil, 131 
Bone Pitch, 251, 252 
Bookbinders’ Varnish, 234 
Borate of Manganese, 240, 243 
Bordeaux Lake, 142 
Brazil Wood, 134 
Bremen Blue, 93 
Brown Hard Spirit Varnish, 233 
Brunswick Black, 251-254 
Blue, 91, 92 
Green, 96-99 
Burgundy Pitch, 164 
Burning Oils, 205 
Burnt Sienna, 64 
Button Lac, 169 


Cadmium Yellow, 79 
Cake, Linseed Oil, 175 
Caleitone, 237 
Calcium Carbonate, 31 

Chromate, 159 

Oxide, 33 

Sulphate, 33 
Calespar, 31 
Calsomines, 17-20, 158 
Camphor Oil, 208 
Canada Balsam, 163, 164 

Turpentine, 163 
Candlenut Oil, 192 
Caput Mortuum, 109 
Carbon Bisulphide, 212 

Black, 130 

Tetra: chloride, 213 


©cos § Oatmine Lake, 133 


Caro, on Fluorescein, 135 


.q Casein, 17 
«.4 Cassel Brown, 123, 124 


Yellow, 79 


Caustic Potash, Specific Gravity of, 265 
Soda, Specific Gravity of, 265 
Cawree Gum, 170 
Celestial Blue, 91 
Celluloid Varnishes, 236 
Cellulose Acetate Varnishes, 237 
Chalk, 31 
Charlton White, 52 
China Clay, 34 
Chinese Blue, 77, 85-89 
Ink, 129 
Red, 74 
White, 48 
Wood Oil, 187-189 
Chloroform, 210, 212 
Chromate of Lead, 65 
Chrome Ochre, 61 
Chrome, Lemon, 71 
Middle, 72 
Orange, 73 
Primrose, 71 
Red, 74 
Yellow, 65-72 
Chromes, Analysis of, 75, 76 
Specification for, 74 
Claret Lakes, 144 
Coal Tar Dye-stuffs, 135 
Naphtha, 214 
Pitch, 251, 252 
Cobalt Acetate, 240, 245, 250 
* Blue, 92, 93 
Driers, 245 
Estimation of, 249 
Linoleate, 240, 245, 247, 250 
Resinate, 240, 247, 250 
Yellow, 79 
Cochineal Lakes, 133, 134 
Colcothar, 109 
Cold Water Paints, 17-20 
Colloid Mill, Plauson’s, 61 
Cologne Earth, 123, 124 
Colophony, 161-163 
Coloured Resins, 172 
Colour House Plant, 66, 67 
Colours, Gold-size, 10 
Colours, Graining, 10 
Paste, 7 
Staining, 10 
Common Black Varnish, 252 
Frankincense, 163 
Resin, 160-163 
Composition of Linseed Oil, 174, 175 
Concentrated Driers, 247, 248, 249 
Congo Copal, 172 
Copal, Angola, 171 
Benguela, 171 
Congo, 172 
Kauri, 170 
Manila, 167, 233 
Sierra Leone, 171 
Pontianac, 171 
Copperas, 87, 109 








INDEX 


Copper Blues, 93 

Corn Oil, 192 

Cotton Seed Oil, 182 

Covering Power of Pigments, 157 
Cowdee Gum, 170 

Crimson Lakes, 133, 134, 144 
Cyprus Umber, 121 


Dammar Varnish, 235 
Dammar, Black, 166 

Gum, 166 
Derby Red, 74 
De Pierre on Paris Blue, 85 
Diazo Dye-stufis, 136, 187, 141-143 
Diazo Solution, 142 
Dichlorethylene, 215 
Dichlorhydrin, 215 
Diesbach on Paris Blue, 85 
Dippel’s Oil, 131 
Dipping Paints, 10, 34 
Distempers, 17 

Analysis of, 20 

Dry ii 

Paste, 18 

Properties and Uses, 19 
Distillation Test on Turpentine, 198 
Dope, 237 
Dragon’s Blood, 173 
Driers, 239-250 

Dry, 248 

Liquid, 246, 248 

Paste, 247, 248 
Drop Black, 131 
Dry Distempers, 17 
Drying of Colours, 68 
Drying Oils, 174 

Room, 68 
Dutch Pink, 134 


Earth, Green, 94, 95, 136, 139 

White, 35, 136, 139 
Elemi, 164, 165 
Elutriator, 30 
Emerald Green, 102-105 
Enamels, 8 
Enamel White, 52 
Enamel, Flatted, 9 

Paints, 8 
Engler Distillation Flask, 198 
English White, 31 
Kosin, 135, 141 
Epichlorhydrin, 215 
Ester Gums, 163 
Estimation of Water in Paints, 24 
Ether, 212 
Ethyl Alcohol, 208 
Euxanthic Acid, 79 
Extenders, 2, 27, 29 
Extraction of Linseed Oil, 175 


Felspar, 34 
Ferric Ferrocyanide, 87, 88 


271 


272 THE CHEMISTRY OF PAINTS 


Ferrous Ferrocyanide, 87 
Ferrous Sulphate, 7, 109, 110 
Filter Presses, 67, 220 
Fineness of Pigments, 152 
Fireproof Paints, 20 
Fish Oils, 182, 190 
Fischer, Otto, on Malachite Green, 135 
Flake White, 39 
Flash Point, 197 
Flat Drying Black Japans, 254 
Drying Paints, 2 
Enamels, 9 
Stone Grinding Mills, 5 
Flatting Varnish, 223 
Fluorescein, 135 
Forkin on Driers, 239 
Frankfort Black, 131 
“Frankincense, 163 
Free Acidity, Determination of, 178 
French Chalk, 35 
Driers, 248 
Ochre, 61, 63 
Polish, 232, 233 
Turpentine, 201 
Fungus on White Lead Paints, 14, 15 
Fusel Oil, 211 


Galipot, 163 
Gamboge, 172 
Garnet Lac, 167, 169 
Gas Carbon Black, 130 
Genuine Chromes, 71-73 
German Black, 131 
Gilsonite, 251, 252 
Glazing, 10 
Glue, 20 
Glycerine Rosin Ester Gums, 163 
Gmelin’s Blue, 92 
Gold Lacquer, 234 
Golden Ochre, 61 
Gold-size, 10, 223, 240 
Graphite, 126, 127 
Artificial, 127 
Grass-tree Gum, 173 
Gravimetric Analysis, Factors in, 260, 261 
Green, Brunswick, 96-98 
Chrome, 96 
Chromium Oxide, 100 
Copper, 101 
Copperas, 109 
Earth, 94, 95, 136, 139 
Emerald, 101-105 
Imperial, 101 
Milori, 96 
Mineral, 107 
Pale, Middle and Deep, 97 
Paris, 101 
Scheele’s 105 
Schweinfurth, 102 
Ultramarine, 82 
Veronese, 94 
Zine, 99 








Green Verditer, 107 
Griess, Peter, on Diazotising, 136, 141 
Grinding Machinery, 4 
Gum Accroides, 173 
Animi, 170 
Benzoin (Benjamin), 165 
Grass-tree, 173 
Kauri, 170 
Thus, 163 
Gypsum, 33 


Hematein, 135 

Hematite, 109 

Halphen’s Colour Test, 182 
Hanus Solution, 181 

Hankow Wood Oil, 187 
Hartley on Driers, 239 

Heavy Spar, 28 

Helio Fast Red B L (Bayer), 143 
Hemp Seed Oil, 191 

Hiding Power of Pigments, 156 
Hofmann’s Violet, 135 
Hydrometry, 262 


Ice Colours, 142 
Iceland Spar, 31 
Imitation Red Lead, 116 
Imperial Green, 102 
Implement Paints, 10 
Indian Ink, 129 
Ochre, 61 
Reds, 110, 111 
Yellow, 79 
Indigo, 136 
Industrial Spirit, 210 
Inert Pigments, 2, 27 
Inside Varnishes, 216, 217 
Insoluble Pigment Dye-stufis, 146 
Todine Value, Determination of, 180 
Tron Oxides, 108 
Italian Ochre, 61 
Ivory Black, 130, 131 


Japans, 8 
Black, 251 
Japan Driers, 246 
Gold-size, 223 
Japanese Ink, 129 
Wood Oil, 187 
Jet Black, 131 


Kalsomines, 17 

Kaolin, 34 

Katanol (Bayer), 140 

Kauri Gum, 170 

Kerosene, 205 

Ketones, 211 

Kieselguhr, 35, 81 

King’s Blue, 93 
Yellow, 79 

* Kish,” 127 

Klein, C. A., on White Lead, 39 


Knight’s Patent Zine White, 52 
Kremnitz White, 39, 44 


Lac, 167, 173 
Button, 167, 169 
Dye, 167 
Garnet, 169 
Seed, 167 
Stick, 167 
Lacquer, Chinese (Japanese), 238 
Lacquers, 234, 235 
Lake, Alizarine, 145, 146 
Lake, Alpha Naphthylamine, 142 
Black, 135 
Bordeaux, 142 
Carmine, 134 
Claret, 144 
Crimson, 133, 134, 144 
Madder, 134 
Munich, 133 
Para-Nitraniline, 142 
Pigments, Analysis of, 146-149 
Purple, 134 
Red P, 145, 149 
Scarlet, 134 
Venetian, 133 
Vienna, 133 
Lakes and Lake Pigment Colours, 133 
Lakes from Synthetic Dye-stuffs, 135-150 
Lamp Black, 128, 132 
Lapis lazuli, 80 
Lead Acetate, 1, 47, 239, 241 
** Lead Bottoms,” 47 
Carbonate, 39 
Driers, 239-242 
Linoleate, 239, 242 
Resinate, 239, 241, 242 
Sulphate, 47 
Tungate, 239, 242 
Leaded Zine Oxides, 48 
Lemon Chrome, 71 
Shellac, 168 
Levigation, 60 
Liebermann-Storch Test, 182 
Light Oils, 205 
Light Spar, 33 
Lime, 17, 33 
Blue, 85 
Linseed Oil, 174-187 
Composition of, 174 
Litharge, 239, 240 
Lithographic Varnish, 225, 226 
Lithol Red R, 143, 144, 148, 149 
Fast Scarlet R., 143 
Lithopone, 19, 52-56, 158 
Analysis of, 55, 56 
Darkening of, 54 
Red Seal, 55 
Liquid Driers, 246 
Logwood Extract, 135 
Lovibond Tintometer, 153, 154 
Lubricating Oils, 205 











INDEX 273 


Lumbang Oil, 192 
Luminous Paints, 16 


Madder Indian Red, 111 
Lakes, 134 
Magenta, 135 
Magnesium Silicate, 35 
Maize Oil, 192 
Malachite, 107 
Green, 135 
Manchurian Bean Oil, 189 
Manganese Acetate, 244 
Borate, 243 
Chloride, 244. 
Driers, 240, 242-245 
Dioxide, 242 
Hydroxide, 244 
Linoleate, 244 
Resinate, 244 
Sulphate, 243 
Tungate, 244 
Manila Copal, 167 
Manjak, 251, 252 
Marble, 31 
Marl, 31 = 
Massicot, 114, 115 
Mastic, 165 
Matt Paints, 2 
Mauve, 135 
Menhaden Oil, 190, 191 
Metallic Paints, 15 
Methyl! Alcohol, 210, 211 
Methylated Spirits, 209 
Mica, 34 
Mills, Cone, 6 
Edge-Runner, 5 
Flat Stone, 5 
Roller, 4 
Milner’s Process for White Lead, 44 
Milori Blue, 89 
Green, 96 
Mineral Blacks, 126 
Green, 107 
Turpentine, 203 
Minium, 114 
Mixed Ketones, 211 
Mixing Machinery, 6 
Monolite Red R (B.D.C.), 143, 150 
Montgomery, White Lead, 45 
Mordant Dye-stuffs, 145, 146 
Mountain Green, 107 
Blue, 93 
Miilder on Driers, 239 











Naples Yellow, 79 
Naphtha, Coal Tar, 214 
Shale, 213 
Wood, 210 
Naphthol Green, 138, 139 
Negative Varnish, 234 
Nicholson’s Blue, 135 
Nigerseed Oil, 192 


274 THE CHEMISTRY OF PAINTS 


Nitraniline Red, 142 

Nitric Acid, Specific Gravity of, 264 
Nitrocellulose Varnishes, 236 
Non-Drying Oils, 174 
Non-Poisonous White Lead, 47 
Non-Setting Red Lead, 116 


Oak Varnishes, 223 
Ochre, Analysis of, 62, 63 
French, 61 
Red, 109 
Spanish, 61 
Specification for, 62 
Stone, 61 
Yellow, 60-63 
Oil Absorption of Pigments, 61, 154, 155 
Oil Extraction, 175 
Oil, Corn (Maize), 192 
Hemp Seed, 191 
Linseed, 174 
Lumbang (Candlenut), 192 
Menhaden, 190 
Niger Seed, 192 
Perilla, 190 
Poppy Seed, 191 
Rosin, 193 
Rubber Seed, 192 
Sunflower, 192 
Walnut, 191 
Wood (Chinese), 187-189 
Oil of Turpentine, 195-200 
Analysis of, 196-199 
Polymerisation of, 199 
Specification for, 199 
Oils, Burning, 205 
Light, 205 
Oil Varnishes, 216-231 
Analysis of, 227-231 
Hardness of, 229, 230 
Manufacture of, 216-223 
Specification for, 225 
Time of Drying, 228 
Viscosity of, 227, 228 
Wood, 224 
Oleomargaric Acid, 187 
Oleo-Resins, 163 
Orange Chrome, 73 
Lead, 116, 117, 137 
Mineral, 116 
Shellac, 168 
Orr’s Zine White, 52 
Ostwald Viscometer, 227 
Oxide of Antimony, 58, 158 
Tron, 108 
Tin, 59 
Titanium, 56-58, 158, 159 
Oxide, Black, 126 
Red, 111 


Paint-Destroying Fungus, 14, 15 
Paint Mediums, 1, 21 
Paints, Aluminium, 15 





Paints, Analysis of, 21 
Anti-Corrosion, 10, 127 
Anti-Fouling, 11-14 
Agricultural, 10 
Coloured, 7, 23 
Composition and Properties, 1 
Dipping, 10 
Durability of, 2 
Enamel, 8 
Estimation of Water in, 24 
Gold, 15 
Implement, 10 
Luminous, 16 
Matt (Flatt), 2 
Metallic, 15 
Physical Tests on, 24 
Purple Oxide, 24 
Spraying, 10 
Varnish, 9 

Paper Varnishes, 234, 235 

Paraffin Oils, 213 
Wax, 213 

Para Nitraniline Lake, 142 

Para Red, 142 

Para Rubber Seed Oil, 192 

Para Toner, 142 

Paris Blue, 85, 89 
Green, 101 
White, 31, 32 

Paste Distempers, 19 

Pentachlorethane, 215 

Perchlorethylene, 215 

Perilla Oil, 190 


Perkin, W. H., on Synthetic Dye-stuffs, 135, 


136 
Perkin’s Violet, 135 
Permanency of Pigments, 157, 158 
Permanent White, 27 
Persian Gulf Red, 108, 113 
Persian Red, 74 
Petrifying Liquids, 9 
Petroleum, American, 204 
Distillates, 203-208 
Ether, 205 
Jelly, 204 
Pitch, 204, 251 
Phloxine, 135 
Photographers’ Varnish, 234 
Physical Analysis of Pigments, 151-159 
Physical Tests on Paints, 24 
Pigmented Dope, 237 
Pigment Red B, 142 
Pigments, Covering Power of, 157 
Fineness of, 152, 153 
Hiding Power of, 156 
Inert, 2 
Oil Absorption of, 154 
Permanency of, 157, 158 
Specific Gravity of, 151, 152 
Strength of, 155, 156 
White, 27 
Pinene a and #3, 201 


Pink, Dutch, 134 
Rose, 134 
Pipe Clay, 34 
Piuri, 79 
Plaster of Paris, 33 
Plauson’s Colloid Mill, 61 
Polymerisation of Turpentine, 199 
Wood Oil, 188 
Polymerised Oils, 2 
Poppy Seed Oil, 191 
Pontianac Copal, 171 
Porcelain White, 52 
Potash Felspar, 34 
Potassium Ferric Ferrocyanide, 88 
Potassium Ferrocyanide, 86 
Ferrous Ferrocyanide, 88 
Potassium Hydrate, Specific Gravity, 265 
Potato Spirit, 209 
Precipitated Barium Sulphate, 36 
Precipitation Vats, 67 
Primrose Chrome, 71 
Prussian Blue, 85-91 
Analysis of, 90, 91 
Prussiate of Potash, 86 
Pugging Machines, 4 
Purple Oxide, 110 
Purree, 79 


Quartz, 34, 35 
Quercitron Bark, 134 
Quicklime, 33 


Raw Linseed Oil, 174-182 
Substitutes, 186 

Raw Sienna, 63, 64 
Umber, 121 

Realgar, 79 

Red Lead, 114-116, 137, 239, 241 
Imitation, 116 
Non-Setting, 116 
Substitute, 116 

Red Ochre, 111 

Red Oxides, 108-114 

Red Oxide, Indian, 109, 110, 113 
Persian Gulf, 108 
Spanish, 108 
Turkey, 109, 110 
Vandyke, 109, 111 
Venetian, 33, 110 

Reduced Chromes, 71-73 

Red Ruddle, 111 

Red Sanders Wood, 172 

Refined Linseed Oil, 183 

Refractive Index, 182 

Refractometer, 182 

Resinates of Cobalt, 163 

Resinates of Lead, 163 
Manganese, 163 

Resins, Soft, 160 
Hard, 169 

Resorcin Dye-stufis, 141 

Rhodamines, 135 


INDEX 275 


Roller Mills, 4 
Rose Bengal, 135 
Pink, 134 
Rosin, 22, 160-163 
Analysis of, 162 
Esters, 163 
Oil, 193 
Spirit, 193, 213 
Varnishes, 9, 22, 223, 224 
Alcoholic Spirit, 223, 234 
Rubber Seed Oil, 192 
Ruddle, Red, 111 
Russian Turpentine, 201, 202 
Deodorisation of, 201 





Sandarac, 166 
Sandal Wood, Red, 172 
Sanders Wood, Red, 172 
Saponification Value, 179 
Satin White, 37 
Scarlet Lake, 138 
Scheele’s Green, 12, 105 
Schrétter CO, Apparatus, 32 
Schweinfurth Green, 102 
Schwerspat, 27 
Scumbling, 10 
Seed Lac, 167 
Semi-drying Oils, 174 
Sepia, 124 
Shale Spirit (Naphtha), 12, 13, 213, 214 
Sharple’s Varnish Centrifuge, 220 
Shellac, 167-169 
Bleached, 168, 169 
Button, 167, 169 
Garnet, 167, 169 
Orange, 168 
White, 168 
Shellac Gold-size, 223 
Varnish, 232, 233 
Sienna, Burnt, 64 
Raw, 63 
Sierra Leone Copal, 171 
Siccatives, 239-250 
*“ Sissing ” of Varnishes, 204, 225 
Sitara Fast Red, 143 
Size Distempers, 18 
Skinning of Paints, 7 
Smalts, 92 
Soda Ultramarine, 81 
Sodium Hydrate, Specific Gravity of, 265 
Softening Agents, 233, 237 
Soft Resins, 160 
Solubility Tables, 266 
Soluble Blue, 92 
Soluble Vandyke Brown, 124 
Solutions for Volumetric Analysis, 261 
Solvents and Diluents, 194 
Solvent Naphtha, 214 
Soxhlet’s Apparatus, 21 
Soya Bean Oil, 189, 190 
Spar Varnish, 225 
Specification for American Turpentine, 199 





276 THE CHEMISTRY OF PAINTS 


Specification for Boiled Linseed Oil, 185 


Brunswick Greens, 98 
Burnt Turkey Umber, 123 
Carbon Black, 130 
Emerald Green, 105 
Lead Chromes, 74 
Lithopone (30%), 56 
Ochre, 62 
Oil Varnishes, 225 
Paste Driers, 248 
Prussian Blue, 91 
Raw Linseed Oil, 182 
Red Lead, 116 
Red. Oxide of Iron, 113, 114 
Sienna, 64 
Terebine, 246, 247 
Umber, 123 
Vegetable Black, 129 
Vermilion, 120 
White Lead, 46, 47 
White Spirit, 207 
Wood Oil, 188 
Zine Chromes, 78 
Zine Greens, 100 
Zine Oxide, 52 
Specific Gravity of Liquids, 178 
Pigments, 151, 152 
Spirits of Turpentine, 195-200 
Wine, 209 
Spirit, Potato, 209 
Spirit Varnishes, Analysis of, 236 
Spraying Paints, 10 
Stand Oil, 2, 225, 226 
Stearin Pitch, 251, 253 
Steatite, 35 
Stick Lac, 167 
Stippling, 17 
Stoving Blacks, 251, 253 
Varnishes, 223 
Strength of Pigments, 155 
Sublimed Blue Lead, 48 
White Lead, 48 
Sulphate of Lead, 47-48 
Sulphate of Manganese, 243 
Sulphate Ultramarine, 81 
Sulphite Turpentine, 202 


Sulphuric Acid, Specific Gravity of, 263 


Sulphuric Ether, 212 
Sulfopone, 55 

Sunflower Oil, 192 
Sweated Pitches, 253 
Swedish Turpentine, 201 
Synthetic Alcohol, 210 


Table of Solubilities, 266 
Tale, 35 

Tamol N (B.A.S.F.), 140 
Tannin Lakes, 139 

Tartar Emetic Lakes, 139 
Terebene (Terebenum), 203 
Terebine, 246, 247 
Terpineol, 215 





Terra Alba, 17, 33, 137 
Terra Verte, 94 
Tetrachlorethane, 215, 237 
Thermometric Tables, 260 
Tin Oxide, 59 
Tintometer, 153, 154 
Titanium Dioxide, 56-58 
White, 56-58 
Triacetin, 237 
Trichlorethylene, 215 
Triphenylphosphate, 237 
Tungate of Lead, 239, 242 
Manganese, 244 
Turkey Red Oxide, 109, 113 
Turnbull’s Blue, 92 
Turpentine, American, 195-200 
Analysis of, 196 
French, 201 
Portuguese, 202, 203 
Regenerated, 203 
Russian (Swedish), 201 
Substitutes, 203- 208 
Sulphite, 202 
Tuscan Red, 111 
Twaddel Hydrometer, 262 
Twitchell’s Process, 182 


Ultramarine Blue, 33, 34, 80-85 
Analysis of, 84, 85 
Cobalt, 92 
Cobalt Shade, 83 
Constitution of, 84 
Manufacture of, 81 
Properties and Uses of, 83 

Umber, Analysis of, 122 
Burnt, 121-123 
English, 121 
Raw, 121 
Specification for, 123 
Turkey, 121-123 


Unsaponifiable, Determination of, 179 
Vacuum Drying Stoves (Scott’s), 68, 69 


Vanadium Driers, 245, 246 
Vandyke Brown, 123, 124 
Crystals, 124 
Soluble, 124 
Red, 109 
Varnishes, Analysis of, 227, 236 
Body, 217, 222 
Clarification of, 220, 221 
Copal, 217 
Floor, 217 
French Oil, 171, 222 
Inside, 216, 217 
Manufacture of Oil, 216-225 
of Spirit, 232-236 
Rosin, 9, 223, 224 
Spar, 225 
Specification for Oil, 225 
Viscosity of, 225, 227 
Zapon, 237 


Varnish Paints, 9 
Vaseline, 204 

Vegetable Black, 128, 129 
Venetian Red, 33, 110 
Venice Turpentine, 164 
Verdigris, 106 

Verditer, 93, 107 
Vermilion, 117-120 
Veronese Green, 94 

Vine Black, 131, 132 
Violet Lacquer, 235 
Viscometer, Ostwald, 227 
Volumetric Analysis, Solutions in, 261 


Walnut Oil, 191 
Water Paints, 17-20 
Waza Pitch, 251, 253 
Weights and Measures, 258, 259 
White, Antimony, 58, 59 
Chinese, 48 
Titanium, 56-58 
Zine, 48 
White Base, 17 
Earth, 136, 139 
Enamels, 9 
Hard Spirit Varnishes, 233 
Whiting, 17, 31, 32, 137 
White Lead, 39-47, 137 
Analysis of, 46, 47 
Armstrong and Klein on, 39 
Chamber, 42 
French (Clichy) Process, 43 
_ Kremnitz, 44 
Manufacture of, 40 
Milner’s, 44 
Montgomery, 45 
Non-Poisonous, 39 
Properties of, 45 
Specification for, 46 
Stack (Dutch), 40 
Sublimed, 48 
White Oxide of Antimony, 58 
White Paints, 7 
Pigments, 27-59 
Polish, 233, 234 


INDEX 2 





=) 


~~) 


White Shellac, 168, 169 

White Spirit, 203-208 
Analysis of, 206, 207 
Manufacture of, 204 
Specification for, 207 

Wolff, H., on Varnishes, 229, 230 

Wood Alcohol (Naptha), 210, 211 

Wood Oil Varnishes 224, 225 
(Chinese), 187-189 

Wood Tar Pitches, 251 
Turpentine, 200, 201 

Wij’s Solution, 181 


Xylol, 214 


Yellow Ochre, 60-63 
Pigments, 60 

Yellow, Antimony, 79 
Arsenic, 79 
Cadmium, 79 
Cassel, 79 
Chinese, 60 
Chrome, 65 
Indian, 79 
King’s, 79 
Naples, 79 
Zinc, 77 


Zapon Varnishes, 237 

Zinkolith, 52 

Zine Chrome, 77, 78, 99 
Analysis of, 78 
Specification for, 78 

Zine Driers, 248 

Zine Green, 99 

Zine Oxide, 48-52 
Analysis of, 50 
Leaded, 48 
Manufacture of, 49 
Properties of, 50 
Specification for, 52 

Zine Sulphide, 52-56 

Zine White, 48 1 

Zine Yellow, 77, 78, 99 

Zumatic Driers, 248 











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